More than 2,000 pupils were sent home early on police advice, after threats of gang violence outside two schools in south-east London.
Pupils at the Peckham Academy, Peckham, and Harris Girls' Academy in East Dulwich were sent home early on Friday.
Police advised head teachers to end the school day early and said they would step up patrols over the weekend.
BBC London correspondent Guy Smith said it could be linked to the murder of a man in nearby New Cross on Sunday.
Jason Gayle-Bent, 29, was stabbed to death yards from his front door in south-east London, after a gang on bikes rode up to him and fired shots.
Scotland Yard said they had received information about possible violence outside the schools as they were closing on Friday afternoon.
Supt David Chinchen said: "I must stress that the information was very specific and all precautions needed to be taken.
"Fortunately no crimes have taken place."
Police say the situation will be "regularly reviewed" and extra patrols are in place.
But Supt Chinchen added: "There is nothing at this stage to indicate an ongoing problem.
"There is no reason for pupils or parents to be overly concerned and all schools should open as normal next week.
"Obviously, we would ask people to contact police if they hear anything specific around threats but we must ensure that those at the heart of these threats do not succeed in causing unnecessary fear."
Six youths questioned about the murder of Mr Gayle-Bent have since been released on bail.
Two more were arrested on Friday morning and are still being questioned.