Police responded to a fight among a large group of teenagers at Elm Park Primary School around 9pm on Saturday, March 22.
Two boys, 16 and 19, were stabbed with injuries thought to be neither life-threatening nor changing.
Officers arrived “largely outnumbered” and faced hostility, with four police officers being attacked and injured.
Three teenagers – a 14-year-old girl, a 16-year-old boy and a 17-year-old girl – were arrested at the scene on suspicion of assault on an emergency services worker.
They have been bailed while enquiries continue.
Police have added that two more boys, 15 and 17, were arrested in Hornchurch the next day (March 23) on suspicion of possessing an offensive weapon.
A letter written by Simon Hutchinson, neighbourhood policing superintendent for Havering Borough, says the boys had returned to find knives.
It reads: “On the night an increased police presence was put in place and weapons sweeps conducted after extremely valuable information was received from the local community.
“These weapons sweeps extended into Sunday (23rd March) morning and resulted in the retrieval of a number of discarded weapons and two further arrests of individuals, apparently returning to retrieve the discarded weapons.”
The two boys have been bailed pending further enquiries.
Supt Hutchinson adds: “Officers were heavily outnumbered but tried to engage with those present and manage the ongoing pockets of violence that were present.
“They showed tremendous bravery confronting this group despite the numbers and level of potential violence.
“I am proud of the courage that each of those officers showed.
“Going forward my team continue to assess the impact on the local community. We are working closely with the community, local authority and councillors to provide a policing plan that will increase visibility.”
A Metropolitan Police spokesperson added: “An investigation into the circumstances of the incident is ongoing.
“In response to this incident, police patrols in the area are being stepped up at key times. We are working with our partners at Havering Council to understand what occurred, and to ensure that nothing like it occurs again.”
