Officers were called to reports of an assault at Bobby Moore Academy near Queen Elizabeth Park just after 12.30pm yesterday (March 13).
London Ambulance Service crews also attended and found a boy who had been stabbed in the leg.
He was taken to hospital where his condition was assessed as non-life changing.
Three boys were arrested on suspicion of grievous bodily harm and remain in custody.
All pupils were cleared from the building and no other injuries have been reported.
A spokesperson for Bobby Moore Academy said: “Police were called to Bobby Moore Academy this afternoon, following an incident involving a very small number of students.
“One of our students needed hospital treatment and we are expecting they will make a full recovery.
“We are in close contact with the family, fully supporting them and sending very best wishes from the whole school community.
“The safety and wellbeing of our students will always be our top priority, and our staff acted with great professionalism, following all procedures and practices.
“We recognise this will have been upsetting news for our families, and we were in touch with them providing updates throughout the afternoon.”
A spokesperson for Metropolitan Police said: “Police were called to a secondary school, close to Queen Elizabeth Park at 12:33hrs on Thursday, 13 March following reports of an assault.
“Officers attended and three boys were arrested on suspicion of GBH. They remain in custody.
“The victim, a 15-year-old boy has been taken to hospital with a stab wound to his leg.
“His injuries are not deemed to be life-changing.”
