How much responsibility should be assigned to an adolescent who commits acts of juvenile delinquency?
This is a very broad question; there are so many categories of juvenile offenses, and the term "adolescent" can be used to describe kids as young as eleven or twelve up to maybe sixteen or seventeen. Offenses are labeled as "juvenile" when the offender is younger than eighteen. One could probably best begin thinking about this question in terms of a youngster's age, first, and then the severity and frequency of the offense(s) secondly.
It is not unusual for an adolescent to experiment with society's boundaries occasionally. An eNotes/Wikipedia article discusses this research by Moffitt (2006) :
. . . there are two different types of offenders that emerge in adolescence. One is the repeat offender, referred to as the life-course-persistent offender, who begins offending or showing antisocial/aggressive behavior in adolescence (or even childhood) and continues into adulthood; and the age specific offender, referred to as the adolescence-limited offender, for whom juvenile offending or delinquency begins and ends during their period of adolescence.
This is a tricky subject, again because there is so much variance in ages and offenses, but while consequences might vary greatly to account for these differences (i.e. a twelve year old who brings a gun to school should probably not receive the same consequence as a twelve year old who writes his phone number on the bathroom wall), assigning responsibility should not. In other words, adolescents should be held responsible for their delinquent acts in a manner that is appropriate for their age, the severity of the act, and whether, as stated above, he or she is beginning to show signs of consistent antisocial tendencies.