Juvenile cases have no general rule. In juvenile case, the probation office screens the cases to determine if in their opinion charges should be filed. Many times the charges are not filed, but instead the child is placed on information probation without court intervention. If the court does get involved it is because the probation office referred the case to the DA. If the DA files charges then your child will have to go to court,.
If the child is either found guilty of the charges or pleads guilty, then he will be sentenced to whatever the judge feels is right. Juveniles get ankle monitor, probation, time in juvie hall and could even be sent to a group home - even on a 1st offense.
You need an attorney. You should hire one if you have the means. If you do not have the means, then you should gather all the things that make your child seem outstanding, grades, awards, letters of support from people, etc. And put a package together and send it to the probation department and ask them to take the good info into consideration when deciding what to do in regards to the criminal activity.
Your child should under no circumstances answer any questions by the probation officer regarding the facts of the case - another reason an attorney is usually used to try to get the probation office to divert the case away from court.
The above information does not establish an attorney client relationship nor is it meant to provide legal advice.
To prove a second degree burglary charge the D.A. has to prove the minor broke into the school with the intent to commit larceny or any felony. If the minor did not possess any stolen goods then an attorney should push to get the charge reduced to a misdemeanor, assuming there was no major property damage. The punishment will depend on whether he or she is found guilty of a felony or a misdemeanor, the school record and the circumstances of the minor's home situation. At 13 and with no prior referrals to probation there is a good chance the minor could be released to the parent's custody and placed on probation with credit for time served, with a curfew and possibly an ankle bracelet.
Legally this could be charged as a felony and your son faces custody time. In reality, he's unlikely to get convicted because the matter should result in a short period of informal probation followed by a dismissal. I say this matter "should result" in such a favorable outcome assuming you hire an aggressive attorney experienced in handling juvenile cases. There is also a good possibility that this matter could result in an outright dismissal without informal probation if your son is an otherwise upstanding child (good family support, good school attendance, good relations with the school he allegedly burglarized, etc). Hire an attorney asap