Formal Probation (or Supervised Probation) requires the defendant to meet with an assigned probation officer on a regular basis (usually once a month). Informal Probation (or Summary Probation) requires the defendant to complete certain terms of the sentence and stay out of trouble. Scheduled meetings with a probation officer are not necessary under summary or informal probation.

The main difference for your son's future is that since "summary probation" is not available for felonies, the law holds that where one is put on summary probation for a wobbler offense [auto tampering is one], that automatically reduces it to a misdemeanor. Since many attorneys don't know that, somewhere along the line your son needs to point that out, so the record can decree it a misdemeanor. But the technical difference is that one does not have a probation officer to report to on summary; on formal, there are probation reports, checks, etc.