Police were called to Upper Street at 12.40am.
Three boys arrested on suspicion of GBH have been released on bail.
The suspects aged 12, 13 and 15 were taken into custody after reports of a fight involving a “noxious substance” at Dagenham’s Sydney Russell School on Wednesday.
Six pupils were treated for injuries at the Parsloes Avenue school. Two girls and a boy required hospital treatment but were discharged on the same day.
Janis Davies, headteacher of the school rated “outstanding” by Ofsted in 2013, said the suspects would not be allowed back into school until a full investigation had taken place.
The suspects have been bailed to appear at an east London police station in the near future.
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