Substantial evidence supported the finding that the juvenile appellant committed robbery, where appellant and a codefendant approached the victim together, and the codefendant demanded money at knifepoint. Appellant was present at the robbery, stood with the codefendant, and fled together with him after the robbery. He was in the company of the codefendant before the robbery, and was arrested with him afterwards. The juvenile court was not obligated to believe appellant’s testimony that he was merely present at the scene, and the determination of credibility shall not be disturbed on appeal. However, it was an abuse of the juvenile court’s discretion to require appellant to maintain a “B” average as a condition of probation. The record showed that compliance with the condition was beyond appellant’s capacity. The probation condition bore no relationship to appellant’s present or future criminality, was not specifically tailored to his individual circumstances, and was not narrowly drawn to serve the interests of public safety or rehabilitation. However, the requirement that he achieve “satisfactory” grades and attendance could stand.