The latest incident happened on Monday in the playground of Downsview special needs school in Hackney.
Last November the alleged victim was one of two girls sexually assaulted by a fellow pupil in the toilets.
Following that incident the school adopted a policy of escorting the children - who all experience learning difficulties - to the toilets, which were also locked during lessons.
A 12-year-old boy was suspended for two days. Sgt Ian Delbarre, of the area's child protection team, said: 'We decided it was not in the public interest to prosecute.' Police are now investigating the latest incident, which concerns two different boys.
A council inquiry, demanded by the girl's parents after the first incident, found the school had 'acted entirely properly'.Reuse content