An investigation by the BBC claims footage it had obtained showed mistreatment in padded seclusion rooms between 2014 and 2017.
The school said it was co-operating with the police and supporting families.
Whitefield School has more than 300 pupils aged between three and 19, many of whom have severe or complex needs and are unable to communicate verbally.
In a statement, the London borough of Waltham Forest said it had visited the school in 2017 following an Ofsted inspection “to ensure the safeguarding concerns raised were acted upon immediately”.
The Ofsted report rated the school inadequate after pupils were found to be placed in secure rooms for “prolonged periods of time”.
The Metropolitan Police confirmed it had launched an inquiry into “several allegations of child cruelty” at the school between 2014 and 2017 but there had been no arrests.