It’s a lesson in coverups.

State Comptroller Tom DiNapoli’s auditors turned up 428 incidents — from assaults to sexual offenses — the city didn’t report to the state Education Department in the 2012 and 2013 school years, as required by law, he revealed Wednesday.

And that was just in 10 schools that were randomly audited — two in each borough.

“The big concern here is that when incidents don’t get reported or are, in effect, downgraded, schoolchildren are put potentially in harm’s way,” DiNapoli said.

His auditors counted 1,147 incidents in the schools they visited, but only 989 that were forwarded to Albany, he said.

One Staten Island school, IS 27, didn’t report 165 of 408 incidents, the auditors said.

City education officials slammed DiNapoli’s methodology, saying his auditors misinterpreted which incidents required notification to the state.