BAY CITY -- A judge rules for a mistrial in the case of a woman authorities say had sexual relationships with three students she taught while serving as a substitute teacher in Bay City.

Bay County Circuit Judge Joseph Sheeran on Friday granted the request of Heidi Lewis' lawyer after a prosecutor had more specific language added to the charges.

The 43-year-old is charged with six counts of third-degree criminal sexual conduct.

The Midland woman was a substitute at Bay City Central High School, teaching a special education course from January 2010 for several months.

Three of Lewis' students testified Wednesday that they had sex with her multiple times after school ended for the summer.

They were 17 at the time.

A new trial is scheduled for May 1.