The victim remains in a serious condition
A 15-year-old boy was knifed in Marlborough Gardens at around 3.25pm on Friday, 24 September.
He was taken to hospital for treatment. His condition is now serious but stable.
Officers arrested a 17-year-old male from Kent on suspicion of attempted murder yesterday.
He is currently being detained at an east London police station.
Detectives are still appealing for witnesses to come forward.
Anyone with information about the stabbing is asked to call 101 or tweet @MetCC and quote CAD 4545/24Sep.
To remain anonymous, please contact the independent charity Crimestoppers on 0800 555 111.
For more on this story, and the latest on our other local and national news, listen to Time 107.5FM
Tags: Upminster, Metropolitan Police, Stabbing