I had a similar question, but it seems that this question appeals largely to the 'justice' model i.e. societal definitions of justice, contrary to conflating the 'justice' and 'welfare' model into the one response.
Your point of argument is an individualistic conception, though it is important to ensure that your argument logically coincides with any utilised case law, and I would suggest you to look at the legal system holistically, not just small facets which obscure the the authentic image of juvenile justice.
A primary argument that will comprise a large facet of your essay is that of doli incapax, where conclusive presumption and rebuttable presumption comes in. Is doli incapax, as a legal principle which recognises the gradual development of mens rea within an individual lenient/harsh relative to societal standards? As is the norm, incorporate cases/articles/statistics to support your argument. You can use the case of R v LMW 1999 (the Corey Davis case) where since this is a case of rebuttable presumption, the prosecution (regina) is additionally burdened to show that the defendent is not only responsible in practicality (actus reus) but that they possess criminal responsibility (mens rea), i.e. that they understand the wrongness of their crime. Is this perhaps an insurmountable burden? Is this case, where the accused was acquitted, an obstruction of justice relative to societal standards? Use articles to formulate your argument, not substantiate a preprepared argument.
A sentence on a juvenile must be proportionate to the crime, and unlike the adult court, rehabilitation is given much greater emphasis as a mitigating factor of sentencing. The case of R v GDP (1991) is an exemplary demonstration of the importance of rehabilitating young offenders and facilitating their reintegration into society, where this case was reviewed, and given the offenders demonstrations of rehabilitation by placing an emphasis on his education and not reoffending, a twelve month custodial sentence for damaging property was appropriately substituted for a twelve month probationary sentence. Relative to the aims of the Juvenile Justice System, to control crime through punishment and deterrence, discretionary power through 'applying principles and values to facts' (Nick Cowdrey) allowed the welfare model to be effectively fulfilled. Though the substitution to a non-custodial sentence is an imposition of leniency, as it unburdens the young offender (defendant) of accountability due to the unrestricted nature of a probationary sentence.
As you can see, by combining two opposing arguments, you can subsequently reach a mutual ground by stating the law exhibits a varying degree of effectiveness, though only do this within reason (i.e. having appropriate case law/legislation/articles/statistics to substantiate your argument as demonstrative above).
An important aspect of your essay will be diversionary schemes where young offenders are subjected to non-judicial processes (alternatives to court), which are statutorily empowered under the Young Offenders Act 1997 (NSW). Diversionary schemes in ascending hierarchy are, warnings directed by the NSW police, formal cautions directed by the NSW police, and Youth Justice Conferences directed by the Department of Juvenile Justice.
You can proceed to highlight the effectiveness of such diversionary schemes to the rehabilitation of the offender. This is where your response revolves around statistics and articles because case law means that the case entered the court, and diversionary schemes is about subverting the offender from the court. If the contemporary statistics state that certain alternatives to court result in the rehabilitation of the majority of offenders and thus obstructs their prospect of reoffending, then your argument will be although its effective, it is considered as lenient in accordance with societal standards, as evident in the article .... Then you can outline s.8 of the Young Offenders Act which lists the offences which cannot be subjected to diversionary schemes, such as offences that cause the death of a person, indecent assault, aggravated indecent assault etc...
Ensure that your argument is concise, do not include an unnecessary abundance of discourse, and do not manipulate your legislation/articles/cases to fit your ideas of the juvenile justice system. They dictate your argument.