The incident happened in South Lambeth Road near Heyford Avenue just after 5.40pm on April 27.
Officers and London Ambulance Service crews attended and found a boy who had been stabbed.
He was taken to hospital for treatment where his injuries were assessed as non-life threatening.
No arrests have been made as police enquiries continue.
A spokesperson for Metropolitan Police said: “Police were called at 5.42pm on Sunday, April 27, to South Lambeth Road, Stockwell, following reports of a serious assault.
“Officers and the London Ambulance Service attended and a 16 year old boy was taken to hospital with stab wounds.
“Their condition was assessed as non-life-threatening or life-changing.
“Enquiries are ongoing – anyone with information is asked to call police on 101 quoting CAD 5193/27APR.
“Alternatively, you can contact the independent charity Crimestoppers anonymously on 0800 555 111 or visit crimestoppers-uk.org.
