The teen admitted to charges of false imprisonment, reckless endangerment and simple assault - all misdemeanors. He faces a dispositional hearing in early March.
He will remain in detention until at least that time.
Also on Thursday, a judge ordered the five juveniles who previously admitted taking part in the videotaped bullying of the 13-year-old to abide by a curfew and 45 days of home monitoring.
The teens also were ordered to perform community service after admitting their roles in return for having the most serious charges against them dropped.
They received curfew restrictions ranging from 60 to 90 days and were released to their parents.
A seventh teen involved, who taped the beating with a cell phone, had all charges dropped.
The victim, Nadin Khoury, recovered from the attack and went on to make numerous TV appearances, including a segment on ABC's "The View" where he met some of the Philadelphia Eagles.