It happened just after 8:30 a.m. on the 4900 block of Knox Street in Germantown.
Police rushed the 16-year-old boy to the hospital. He is listed in stable condition.
Fitler Academics Plus school was placed on a precautionary lockdown as investigators worked the scene nearby.
The lockdown was lifted about 30 minutes later.
No arrests have been made. The shooting remains under investigation.