T EACHERS hurled insults like "bastard," "damn dumb," " 'tard" and "a hippo in a ballerina suit." A bus driver threatened to slap one child. A bus monitor told another, "Shut up, you little dog!"

They were all special-needs students, and their parents all learned about the verbal abuse the same way - by planting audio recorders on the children before sending them off to school.

In cases around the country, suspicious parents have been taking advantage of convenient, inexpensive technology to tell them what children, because of their disabilities, are not able to express on their own.

This week, two teachers from Horace Mann Elementary School, in Cherry Hill, were fired after Stuart Chaifetz posted clips on YouTube of secretly recorded audio that caught one adult calling his autistic 10-year-old son "a bastard."

In less than three days, the post got 1.2 million views, raising the prominence of the small movement. There have been at least nine similar cases across the country since 2003.

"If a parent has any reason at all to suggest a child is being abused or mistreated, I strongly recommend that they do the same thing," said Wendy Fournier, president of the National Autism Association.

But George Giuliani, executive director of the National Association of Special Education Teachers, said that secret recordings are a bad idea. He said that they could violate the privacy of other children.

"We have to be careful that we're not sending our children in wired without knowing the legal issues," Giuliani said.

Chaifetz said that he began getting reports earlier in the school year that his son Akian was being violent.

Hitting teachers and throwing chairs were out of character for the boy, who is in a class with four other autistic children and who speaks but has serious difficulty expressing himself. Chaifetz said that he talked with school officials and had his son meet with a behaviorist. There was no explanation for the way Akian was acting.

"I just knew I had to find out what was happening there," he said. "My only option was to put a recorder there. I needed to hear what a normal day was like in there."

On the recording, he heard his son being insulted - and crying at one point.

With more parents taking such action, he said, fewer educators may get out of line with the way they treat students who cannot speak up for themselves.

"For the tiny percentage of teachers that do it, I hope that they live in fear every day that a kid's going to walk in with a recorder," he said.

He gives just one caveat: "Make sure it's legal in your state."