After admitting to sufficient facts before a Juvenile Court judge with respect to two counts of indecent assault and battery on a person fourteen or older, the juvenile filed a motion seeking relief from the obligation to register as a sex offender pursuant to G. L. c. 6, § 178E (/) (§ 178E [/]). After a hearing, the judge denied the motion, thereby requiring the juvenile to register with the Sex Offender Registry Board (board). We consider here the juvenile’s petition for relief pursuant to G. L. c. 211, § 3. The principal issue he raises concerns the standard by which a Juvenile Court judge determines the risk of reoffense on the part of a juvenile under § 178E (j), an issue that this court considered in Commonwealth v. Ronald R., 450 Mass. 262, 267-268 (2007). We seek to provide additional guidance concerning that standard in this opinion. We affirm the order denying the juvenile’s motion for relief from registration.
Background1 On the afternoon of May 9, 2013, the juvenile, who was then sixteen years old, approached an adult woman from behind as she was walking her dog in Lynn and pulled down the sweatpants she was wearing to her thighs. The juvenile then made a vulgar comment about the victim’s private parts, grabbed his own genitals, and ran away. The woman described her assailant to the Lynn police.
Eight days later, on the afternoon of May 17, 2013, a different woman was walking four children home from school in Lynn when she felt the juvenile touch her buttocks and pull her pants to the ground. The woman called the police and provided a description of her assailant, and soon thereafter, a Lynn police officer observed the juvenile, who fit this description, on a different street from where the incident had occurred. Lynn police patrol units then stopped the juvenile. At a showup identification *171procedure soon thereafter, the second woman identified the juvenile as the person who had pulled her pants down. The juvenile was placed under arrest and taken to the Lynn police station.
After having the opportunity to speak with his mother, the juvenile agreed to speak with the police. He admitted that he had pulled down the second woman’s pants, and when the police mentioned the first woman to the juvenile, he admitted that he had pulled down her pants as well.2 Discussing the second incident, the juvenile explained that he had bought and smoked some marijuana that morning (May 17), and then, while walking, he “just went up to [the second woman] and pulled down her pants.” The juvenile did not give a reason for pulling down the second woman’s pants, saying only that he “just felt the excitement.” The juvenile also did not give a reason for targeting the first woman.
On May 20, 2013, two complaints issued from the Essex County Division of the Juvenile Court Department charging the juvenile with two counts of indecent assault and battery on a person fourteen years of age or older and one count of disorderly conduct. On January 21, 2014, at a hearing before a Juvenile Court judge, the juvenile admitted to sufficient facts with regard to each charge and entered a plea that the judge accepted.3 Between this hearing and the final disposition of the case, the juvenile filed a motion for relief from the obligation to register with the board, and an evidentiary hearing on the motion was held on February 27, 2014.4
At that hearing, the juvenile sought to establish that he did not “pose a risk of reoffending or a danger to the public,” and therefore should be relieved of the obligation to register. G. L. c. 6, § 178E (/). *172He offered the report and testimony of his expert witness, Dr. Barbara Quiñones, a forensic psychologist. Quiñones testified to having administered a “guided clinical instrument” called the Estimate of Risk of Adolescent Sexual Offense Recidivism (ERASOR), a test that she described as “strongly validated” by substantial research as an appropriate risk assessment tool for juvenile sex offenders.5 According to Quiñones, the ERASOR enumerates twenty-five factors that have been “consistently shown to be associated with risk of re-offense,” and in administering the test to the juvenile, she scored each factor as “present, not present, [or] partially present.” She found that in the juvenile’s case, four of the twenty-five risk factors were present,6 twenty risk factors were not present, no risk factors were partially present, and the presence of one factor was “unknown.” Based on her evaluation of the juvenile, which included a lengthy interview with him, a discussion with the juvenile’s mother, the administration of the ERASOR test, and other evaluative processes, Quiñones saw no sign of deviant sexual behavior in the juvenile, in part because in her opinion such a diagnosis requires a finding of six months of deviant behavior — a period of time far longer than that involved in the juvenile’s case. She also stated that in her opinion, based on research she described, the juvenile’s lack of insight into why he committed the two offenses was not indicative of a higher risk of reoffense. Based on her evaluation, Quiñones concluded that the juvenile’s “risk to re-offend sexually is low,” adding that, in forensic psychology, “there is no category of no risk,” and that “[o]nce someone has committed a sexual offense, the lowest category would be low.” She opined that the juvenile’s risk of reoffense was so low that he should not be required to register as a sex offender.
At a hearing in April, 2014, the judge denied the juvenile’s motion for relief from registration and proceeded to set out oral findings and reasons. She described in some detail the facts of the two assaults on the two women, and stated that she found Quiñones’s testimony “thoughtful,” but did not credit the expert’s *173opinion about the juvenile’s lack of sexual deviance. The judge also rejected Quiñones’s ultimate conclusion that the juvenile posed a low risk of reoffense, “based primarily on the facts and the circumstances” of the offenses, which the judge characterized as “egregious.” She stated that this “was a broad daylight sexual assault on two strangers in our community with no apparent measure of restraint” or “any understanding of why he committed these offenses.” The judge determined that the juvenile posed a risk of reoffense and would be required to register with the board.7
The juvenile thereafter filed in the county court his petition pursuant to G. L. c. 211, § 3, seeking relief with respect to the order denying him relief from the obligation to register as a sex offender. The single justice stayed the judge’s order requiring registration and reserved and reported the matter to the full court.
Discussion. 1. Juvenile’s petition for relief under G. L. c. 211, §3. Asa threshold matter, the Commonwealth contends that there is no issue properly before the full court for review, because the juvenile, in the Commonwealth’s view, has abandoned the claim he raised in his petition for relief under G. L. c. 211, § 3, that he filed in the county court. The argument fails. Although this court has deemed an argument waived where it was not raised either before the trial judge or in a G. L. c. 211, § 3, petition for relief, see Paquette v. Commonwealth, 440 Mass. 121, 124 n.3 (2003), cert, denied, 540 U.S. 1150 (2004), that is not the case here. The juvenile previously has raised the substance of the claims he presents to this court, either in the Juvenile Court or before the single justice. In any event, the single justice has reserved and reported the case to this court, and it is properly before us. See Burke v. Commonwealth, 373 Mass. 157, 159 (1977). Cf. Commonwealth v. Goodwin, 458 Mass. 11, 14-15 (2010).8
*1742. Standard for obtaining relief from registration. Under the sex offender registration act, G. L. c. 6, §§ 178C-178P (act), sex offenders, whether adults who have been convicted of a “sex offense” within the scope of the act or juveniles adjudicated as a youthful offender or delinquent on account of committing a qualifying sex offense, are required to register as sex offenders with the board, unless relieved of doing so under one of three statutory exemptions — of which § 178E (f) is one. See Ronald R., 450 Mass, at 264 (“there is a presumption that sex offenders must register” under act). Section 178E (f) provides in relevant part:
In the case of a sex offender who has been convicted of a sex offense or adjudicated as a youthful offender or as a delinquent juvenile by reason of a sex offense, on or after December 12, 1999, and who has not been sentenced to immediate confinement, the court shall, within [fourteen] days of sentencing, determine whether the circumstances of the offense in conjunction with the offender’s criminal history indicate that the sex offender does not pose a risk of reoffense or a danger to the public. If the court so determines, the court shall relieve such sex offender of the obligation to register under [§§] 178C to 178P, inclusive.”9
The juvenile claims that due process requires a judge, in determining under § 178E (f) whether a juvenile should be relieved from the obligation to register as a sex offender based on his or her “risk of reoffense,” to assess the probability of such risk according to an articulated standard that itself is based on objective factors. His argument is that a delinquency adjudication of a *175sex offense together with “the juvenile court’s conclusion as to the propriety for excusing (or [not]) the juvenile’s registration obligation” as a sex offender form the “first step” in the statutory registration process; because this is so, the procedural due process requirements applicable to this registration process come into play; and these must include a requirement that a judge performing the assessment regarding risk of reoffense under § 178E (/) do so according to a defined, objective standard. This is especially important for juveniles, he claims, because of the “historical view of the juvenile justice system as primarily rehabilitative.”
We disagree that a judge’s determination under § 178E (f) whether to relieve a juvenile sex offender from the act’s registration requirements is properly characterized as an integral part of the registration system itself. See Commonwealth v. Shindell, 63 Mass. App. Ct. 503, 505 (2005) (registration requirement is “decision made not by the trial court, but by the ... board”). See also Ronald R., 450 Mass, at 266. But there is no question that the statutory sex offender registration regime prescribed by the act imposes both burdensome and long-lasting requirements on a sex offender that implicate his or her liberty interests.10 There also is no question that, in offering a juvenile sex offender who has not been sentenced to immediate confinement the opportunity to be relieved of the obligation to participate in the registration system in any way, § 178E (f) provides a significant benefit. Accordingly, it is important that the statute’s standards be as clear as reasonably possible.
In Ronald R., after making a delinquency adjudication based on the juvenile’s commission of a sex offense (rape of a six year old child), the Juvenile Court judge imposed a suspended sentence of commitment to the Department of Youth Services until the juvenile turned eighteen and placed the juvenile on probation. Ronald *176R., 450 Mass. at 263. The judge then held a separate nonevidentiary hearing pursuant to § 178E (f) and denied the juvenile’s motion for relief from the obligation to register as a sex offender. Id. at 264. The judge did not make findings, written or oral, but stated that he exercised his discretion under § 178E (f) not to relieve the juvenile from registration based on the facts of the case. Id. at 267, 270. This court rejected the juvenile’s argument that the judge abused his discretion and, quoting § 178E (f), stated that the judge’s “sole task” under the statute was “to ‘determine whether the circumstances of the offense in conjunction with the [juvenile’s] criminal history indicate that the [juvenile] does not pose a risk of reoffense or a danger to the public.’ 11“ Id. at 267.
The juvenile in this case argues that neither the text of § 178E if) nor Ronald R. offers any meaningful guidance about how a Juvenile Court judge is to determine the “risk of reoffense,” creating a statutory regime that permits the standardless and inconsistent exercise of judicial discretion in violation of fundamental concepts of fairness. Cf. BMW of N. Am., Inc. v. Gore, 517 U.S. 559, 588 (1996) (Breyer, J., concurring) (legal standards “must offer some kind of constraint upon a . .. court’s discretion, and thus protection against purely arbitrary behavior”). Particularly for children, for whom the requirement to register as a sex offender may have more profound consequences than for an adult,12 and in light of the rehabilitative focus of the juvenile justice system, the juvenile claims that it is imperative that this court “establish the basic parameters of the term ‘risk’ ” in the statutory phrase “risk of reoffense.” He goes on to argue that at least in the *177context of juvenile sex offenders, the phrase “risk of reoffense” should be measured by whether the offender is “likely” to re-offend, and determined by analyzing factors such as the “seriousness of the threatened harm, the relative certainty of the anticipated harm, and the possibility of successful intervention to prevent that harm.” In support of this standard, the juvenile points to Commonwealth v. Boucher, 438 Mass. 274, 276 (2002), a case involving the sexually dangerous person (SDP) statute, G. L. c. 123A, §§ 1-16.
As previously stated, we agree with the juvenile on the importance of providing a more focused approach to the risk assessment that § 178E (f) calls for, but disagree with his proffered standard. The Commonwealth points out, correctly, that the Legislature did not use the words “likely” to reoffend in § 178E (f), as it did in the SDP statute. See G. L. c. 123A, § 1 (definition of “[sjexually dangerous person”). As the SDP statute demonstrates, if the Legislature had wanted to use the “likely” standard in § 178E GO, it could have done so. See, e.g., Commonwealth v. LeBlanc, 407 Mass. 70, 74-75 (1990) (Legislature’s inclusion of particular language in certain statutes, and omission of such language in statute at issue, indicates affirmative choice not to include that language). Although registration imposes distinct burdens on a sex offender and perhaps particularly a juvenile sex offender, the infringement on personal liberty is far less than if adjudicated an SDP. See Doe, Sex Offender Registry Bd. No. 27914 v. Sex Offender Registry Bd., 81 Mass. App. Ct. 610, 615 (2012). In the circumstances, it is not reasonable to infer that the Legislature intended the phrase, “does not pose a risk of reoffense,” in § 178E (/) to mean, even for a juvenile sex offender, that he or she was not “likely to reoffend.”13
*178In attempting to give more definition to the standard regarding risk of reoffense incorporated into § 178E (/), it is useful to take a somewhat functional approach. We view the standard for determining “risk of reoffense” under § 178E (f) as having two components: (1) the level of risk warranting relief from registration, and (2) the basis on which the judge assesses this risk. We consider each component separately.
a. Level of risk. Despite the statute’s indication that the judge may relieve an offender from registration only if he or she “does not pose a risk of reoffense or a danger to the public,” we do not interpret this language to mean “no risk,” because the absence of any risk is impossible as a matter of logic and common sense. See In re Harold W, Ill. App. Ct., No. 2-12-1235 (2d Dist. Apr. 18, 2014) (unpublished) (interpretation of statute allowing termination of sex offender registration upon showing of “no risk to the community”; “to require proof of the complete absence of any risk would mean that no one would ever be able to satisfy the statute beyond any doubt” because “[tjhere is always a possibility that sex offenders will reoffend”). Moreover, there appears to be a consensus among experts that it is impossible to say that a person who has committed a sex offense — which by definition includes every person potentially subject to registration under the act — poses no risk of reoffense.14’15 We will not attribute to the Legislature the purpose of rendering § 178E (/) meaningless by means of an insurmountable standard for obtaining relief from registration. See Victory Distribs., Inc. v. Ayer Div. of the Dist. Court Dep’t, 435 Mass. 136, 140 (2001); Commonwealth v. Wade, 372 Mass. 91, 95 (1977) (refusing to construe statute such that it “would become a useless legislative exercise”).
Because § 178E (/) itself does not define clearly the appropriate level of risk warranting relief from registration under § 178E (/),
*179we seek guidance on the issue from other sections of the act. See Pentucket Manor Chronic Hosp., Inc. v. Rate Setting Comm’n, 394 Mass. 233, 240 (1985) (“When the meaning of a statute is brought into question, a court properly should read other sections and should construe them together ... so as to constitute an harmonious whole consistent with the legislative purpose” [citation omitted]). See also Care & Protection of Jamison, 467 Mass. 269, 276 (2014); Wolfe v. Gormally, 440 Mass. 699, 704 (2004). General Laws c. 6, § 178K (1), in particular, is pertinent.16 This section directs the board to establish a system by which all sex offenders required to register are classified by risk of reoffense — low, moderate, or high •— according to the factors spelled out in § 178K (1) (a)-{l), and in the board’s implementing regulations, 803 Mass. Code Regs. § 1.40 (2013). See Doe, Sex Offender Registry Bd. No. 68549 v. Sex Offender Registry Bd., 470 Mass. 102, 105 (2014) (Doe No. 68549). See also G. L. c. 6, § 178K (2) (ti)-(c). Section 178K (1) and (2) (a) establishes “low” risk of reoffense as the lowest level of risk classification and, therefore, the threshold level of risk requiring registration. See Doe No. 68549, supra at 112. See also Doe, Sex Offender Registry Bd. No. 24341 v. Sex Offender Registry Bd., 74 Mass. App. Ct. 383, 387 (2009) (Doe No. 24341). A “low” risk of reoffense under § 178K (1) is “not merely a hypothetical or speculative potential risk.” Doe No. 24341, supra at 388. Rather, it is a risk that is “cognizable”17 — i.e., “perceptible”; “[c]apable of being known, perceived, or apprehended by the senses or intellect”18 — and one that can and indeed must be able to be articulated and described based on affirmative evidence. See, e.g., Doe No. 68549, supra at 108; Doe, Sex Offender Registry Bd. No. 1211m. Sex Offender Registry Bd., 447 Mass. 750, 762-766 (2006) (Doe No. 1211). It follows that to qualify for exemption from registration under § 178E (/), a juvenile sex offender’s risk of reoffense should be less than this “low” registration-triggering risk. In other words, it is a risk that is more than “no risk” — and therefore more than hypothetical or purely speculative — but not as definite as what qualifies *180as “low” under § 178K (1).
b. Assessment of risk ofreojfense. We turn to the basis on which a Juvenile Court judge is to make the assessment of risk of reoffense under § 178E (/). The statute specifies that the judge is to determine this risk based on “the circumstances of the offense in conjunction with the offender’s criminal history.” G. L. c. 6, § 178E (/). However, it is silent on the relationship between these two factors and a predictive assessment of risk of reoffense, and in the case of a juvenile sex offender particularly, that relationship is not self-evident.19’20
The link between the circumstances of the offense and criminal history and an offender’s risk of reoffense may be illuminated, however, where, as was the case here, the juvenile presents expert evidence that focuses directly on the question of risk. In this case, for example, Quiñones testified that the juvenile’s targeting of strangers •— shown by the circumstances of the two offenses — indicated a risk of reoffense, but that the juvenile’s commission of two sexual offenses within a brief period (eight days) did not, in her opinion, increase his risk of reoffense because he committed *181the second offense without having been detected as having committed the first.21 If a juvenile does offer expert evidence regarding his or her risk of reoffense — e.g., expert testimony or relevant research studies by experts in the field — the judge should consider that evidence in assessing the “circumstances of the offense” and ultimately determining whether to exempt the juvenile from registration.22 That the judge is not bound to credit proffered expert testimony, see Commonwealth v. DeMinico, 408 Mass. 230, 235 (1990), does not diminish the obligation to give it serious, reasoned consideration. Cf. Bianco v. Bianco, 371 Mass. 420, 423 (1976) (where judge has broad discretion, “it is important that a judge’s findings clearly indicate that [the judge] has weighed all” relevant considerations).
Independent of expert evidence, and especially where no expert evidence is offered, the judge may seek guidance by reference to the factors addressing risk of reoffense in G. L. c. 6, § 178K (1) (a)-(l), and the board’s implementing regulations. More particularly, it may be appropriate for the judge to evaluate the juvenile’s criminal history and the circumstances of his or her offense through the lens provided by these statutory and regulatory risk factors. Consideration, for example, of the juvenile sex offender’s status as a juvenile at the time of the offense and the significance of that status, see G. L. c. 6, § 178K (1) (e), would seem critical in every case. The relevance of other factors will depend on the specific facts presented.23
*182With respect to the process by which a Juvenile Court judge is to reach a decision on risk of reoffense under § 178E (/), as previously mentioned, this section is one of three provisions in the act providing for exemption from registration; the other two are G. L. c. 6, §§ 178E (e) (on Commonwealth’s motion, judge may find that offender need not register) and 178K (2) (d) (board may determine that offender need not register). Section 178K (2) id) specifies that, with respect to the board, it must support a decision to “relieve [an] offender of any further obligation to register” upon “making specific written findings.” The absence of similar language in § 178E (/) indicates that the Legislature did not intend to impose such a requirement. See Ronald R., 450 Mass. at 270 (although sex offender may request written findings, decision whether to issue them rests in judge’s discretion). Rather, by specifying that the trial (or plea) judge is to make the determination concerning the offender’s “risk of reoffense” and exemption from the obligation to register within two weeks of imposing sentence, the Legislature appears to have contemplated that the judge would malee the determination not on the basis of a wholly independent proceeding, but essentially in connection with the resolution of the delinquency proceeding, informed by the knowledge and understanding of the circumstances of both the offense and the offender that the judge had acquired by virtue of being the trial (or plea) judge.24 Cf. Commonwealth v. Ventura, 465 Mass. 202, 212 (2013).
Although a Juvenile Court judge is not obligated to issue written findings under § 178E (f), and although the judge’s process of determining a juvenile sex offender’s relief from registration under this section may be less formal than the process required by the board under § 178K (2) (d), it is important none*183theless for the judge to explain on the record with some specificity the reasons for his or her assessment of risk of reoffense and resulting determination whether the juvenile should be relieved of the obligation to register. Cf. Long v. Wickett, 50 Mass. App. Ct. 380, 402 (2000), quoting Protective Comm. for Indep. Stockholders of TMT Trailer Ferry, Inc. v. Anderson, 390 U.S. 414, 434 (1968) (even where judge has “broad discretion,” it is “essential . . . that a reviewing court have some basis for distinguishing between well-reasoned conclusions arrived at after a comprehensive consideration of all relevant factors, and mere boiler-plate approval phrased in appropriate language but unsupported by evaluation of the facts or analysis of the law”).25 The presence in the record of the judge’s basis for allowing or denying relief from registration is of particular importance where, as here, the juvenile has presented expert testimony or other evidence addressing his risk of reoffense. Cf. Bianco, 371 Mass. at 423.
3. Disposition of present case. The juvenile claims that the judge’s denial of his motion for relief from registration as a sex offender must be reversed because, on the record before her, the judge abused her discretion in rejecting the opinion of his expert witness.
“[Ejxperts’ opinions are not binding on the trier of fact, who may accept or reject them in whole or in part.” Commonwealth v. O’Brien, 423 Mass. 841, 854 (1996) (quotation omitted). See De-Minico, 408 Mass. at 235. The juvenile does not contest this point directly but maintains that the judge nevertheless was obligated to (1) consider “substantial, uncontested expert evidence” concerning the risk of reoffense, and (2) adequately explain any rejection of such expert testimony.
On the first point, the record makes clear that the judge here did consider the opinion testimony of Quiñones, discussing a number of the expert’s specific points or opinions in the judge’s oral findings. As to the second point, the record also shows that the judge *184did explain in general terms her disagreement with some of Quiñones’s opinions. In particular, the judge explained that she did not credit the expert’s opinion that the juvenile’s offenses were not connected to sexual deviance or that marijuana contributed to the juvenile’s offense, based on the judge’s determination that the juvenile committed “a broad daylight sexual assault on two strangers in our community with no apparent measure of restraint” or “any understanding of why he committed these offenses.” The judge stated that these circumstances led her not to have confidence in Quiñones’s opinion that the juvenile’s level of risk of reoffending was low enough to relieve him from the requirement of registration. In both the judge’s initial explanation of her reasons for requiring the juvenile to register and her later explanation of her denial of his motion for reconsideration, the judge emphasized that she had given careful consideration to Quiñones’s testimony and opinions. Although one might take a different view of Quiñones’s testimony and opinions from that of the judge, her rejection of certain of those opinions was neither unexplained nor without any basis.
Furthermore, the judge’s focus in her findings on certain of the circumstances of the juvenile’s offenses — the daylight attacks in the public street on two separate individuals without “apparent... . restraint” and without insight into the reasons for doing so — reflects in substance some of the concerns included in the factors for assessing risk of reoffense set out in G. L. c. 6, § 178K (1), and associated regulations.26 Considering the judge’s findings in light of our discussion in this opinion of the risk of reoffense standard set out in § 178E (/), we cannot say that the findings do not support the judge’s assessment of that risk. In sum, we conclude that based on the record before her, the judge’s ultimate determination that the juvenile should not be relieved of the obligation to register as a sex offender did not lie “outside the bounds of reasonable alternatives,” Adoption of Mariano, 11 Mass. App. Ct. 656, 660 (2010), and, accordingly, did not con*185stitute an abuse of her discretion.27
Judgment affirmed.