The boy has been described as fighting for his life after the attack as he walked along Parsonage Street shortly before 9am on Thursday, April 29.
They found the 13-year-old boy suffering from stab wounds and he was taken to hospital.
Police have not revealed the boy’s condition but a police message sent to neighbours and seen by the Standard described him as critical.
A 15-year-old boy has been arrested on suspicion of causing grievous bodily harm. He remains in custody at an east London police station.
Watch: Mother of 15-year-old who was stabbed to death calls on others to report knife crime
A crime scene remains in place in nearby Mudchute Park.
A Georges Green School statement on their website said: “There was a serious incident in the local community this morning affecting a George Green’s School student.
“We are working with the local authority, the police and other agencies to manage the incident and support all the young people involved.
“The families of any young people who were directly affected have been contacted by the school.
“There is likely to be an increased and more visible police presence in and around the school today.”
A Met spokeswoman said: “Anyone with information is asked to contact police via 101 quoting reference Cad 1321/29Apr.”
Watch: Mothers recall 'hardest call' after sons were stabbed to death