ROCHESTER, N.Y. -- Every day, 60 school bus drivers get into accidents. That's about 22,000 bus crashes a year, injuring thousands of students.

But the problems are much worse than just traffic accidents. A CBS News investigation found a stunning lack of oversight of school bus drivers.

On average, at least once a week a driver is arrested for driving under the influence or child pornography, or even sexually assaulting a child.

A New York couple, who didn't want to be identified, told CBS News that their special-needs daughter was assaulted behind a church by her driver when she was 15.

"When I look into her eyes, I can still see it," her mother said. "He would pick her up, make her get out of the bus and then do whatever he wanted to do."

The family says the driver, Reinaldo Vega, should never have been behind the wheel. He'd been arrested a year earlier on suspicion of child abuse but was allowed to keep his job.

Reinaldo Vega CBS News

The charges were eventually dropped, but Vega pleaded guilty to assaulting their daughter.

"This shouldn't have even been an issue. He just shouldn't have been driving those kids," the mother said.

"The school has an obligation, under the law and morally, to look at what their employees are doing," said Robert King, the family's attorney. "They can't pass the buck, its not okay to push it off on somebody else. They have to do an investigation about what their employees have done in the past and what risk it is to little kids."

School bus drivers have to get a commercial drivers license, but because few drive across state lines, many federal safety rules do not apply. So while drivers with disqualifying medical conditions would not be able to work for a company like Greyhound, they could drive a school bus.

Steve Gursten CBS News

"Truck drivers that are driving heads of lettuce or television sets actually have to meet higher safety standards than the people that drive our children on school buses," said transportation attorney Steve Gursten.

Connecticut and Delaware are the only states that keep track of all drivers arrested on the job. Twenty-one states told CBS News that no school bus drivers had been charged with DUI in the past three years, but we found at least one such arrest in each of those states.

"There are no universal standards. So there is nothing that automatically will disqualify a school bus driver who, let's say, has an extensive criminal background or DUIs or has caused too many crashes," Gursten said.

Alexander Rodriguez was hired to drive a school bus in Tennessee, even though his background check flagged criminal charges in New Jersey for having a weapon and drugs in a school zone.

Alexander Rodriguez CBS News

A few years later he pleaded guilty to the statutory rape of a 15-year-old student who rode his bus.

"Parents assume when they put their children on a school bus that that driver is safe. These parents really need to be asking who's driving their children," Gursten said.

Complicating the situation: Last year, 90 percent of school districts reported a shortage of bus drivers.

Kelly Shane Hooper in a police interview CBS News

One of the largest school bus companies in the country -- Durham School Services -- has turned to Craigslist to find drivers. The company even called former employees like Kelly Shane Hooper, who was hired despite being under investigation for multiple charges of child pornography.

"I got a phone call from my old job. They were offering me my job back because they were short," Hooper said in a police interview. "$12.80 an hour if you can get up here quickly."

The school bus industry refused all our requests for interviews.