EDITORIAL –     Matthew J. Lee, Bostom Globe staff –   A new video camera system is installed above the drivers seat in a Boston school bus. Boston’s school department has offered no evidence that incidents of bullying or other misbehavior have increased to the point where both audio and video surveillance of students on their way to and from school are required.

Yet the school system is in the process of equipping its 750 yellow school buses with both microphones and cameras.

It’s an extreme initiative that unnecessarily infringes on private conversations.

Video recordings are routine and especially useful when it comes to identifying gross misconduct, like physical assault, on the part of bus riders.

But audio recordings are different in tone and tenor. And the city’s policy fails to make that distinction.

It is not even clear how audio surveillance will keep students safer.

It may even have a deleterious effect, according to defenders of civil liberties.

“We’re indoctrinating children to believe that everything they say and do will be recorded by some faceless entity behind glass,” said Kade Crockford, director of the Technology for Liberty project at the American Civil Liberties Union of Massachusetts.

Massachusetts law prohibits surreptitious audio recordings.

The school department likely can remain within the law by posting signs on school buses informing passengers that they are under both video and audio surveillance.

But that doesn’t make it right. Recording every word out of a student’s mouth still raises serious privacy concerns.