Maybe the penalties need to be stiffer to deter this kind of thing.

With guns, it's always more gun control.

Maybe we need more teacher control.
Reduce the teachers out on the street.
Make it harder for criminals to be teachers.
Maybe have a 2 year "waiting period" before a teacher can be hired.
Dna samples from all teachers with fingerprints.
Ankle bracelet monitoring with gps reports.

Something needs to be done, it's getting more prevalent.