School bus drivers, attendants and other co-workers were charged by federal prosecutors Thursday with taking part in an illegal drug ring involving the powerful painkiller OxyContin (search).

According to the indictment, Miami-Dade (search) school employees were among 29 people who used more than 100 forged or fraudulent prescriptions to obtain thousands of tablets of OxyContin from South Florida pharmacies.

No teachers were involved, and there was no evidence of drug sales to children, U.S. Attorney R. Alexander Acosta (search) said.

The school workers were recruited to use their health-insurance cards as part of the scheme, prosecutors said.

Of those charged in the grand jury indictment, five are Miami-Dade school bus drivers, 13 are school bus attendants and one is a former school bus driver now driving a city bus. Two school custodians, a cook and a cashier were also charged, along with a Miami doctor and five other people.

Miami-Dade school officials had no immediate comment on the 84-count indictment, which came days before classes begin Monday.

Those charged face up to 20 years in prison and a $1 million fine for each count of possession of OxyContin with intent to distribute, as well as additional prison time for fraud charges, prosecutors said.

OxyContin is legal if prescribed for treatment of severe chronic pain. But it has become an increasing problem on the black market because crushing the time-release tablets and snorting or injecting the powder yields an immediate, heroin-like high. Hundreds of deaths are blamed each year on overdoses.