Boyd was accused of forcing the girl to have sex in 2006 at Fraser High School, where he was a substitute teacher and track coach. The now-19-year-old woman testified they had consensual sex at least six times.
Roseville District Court Judge Marco Santia ruled Wednesday there wasn't enough evidence to support the charge of third-degree criminal sexual conduct.
The 38-year-old Boyd still faces a case involving a now 16-year-old girl who testified he offered her $5,000 to have sex but gave her only $200.
In that case, he's charged with first- and second-degree criminal sexual conduct and accosting a minor for immoral purposes.