To be more clear...

There should be punishment if there's good reason to think he was doing things for his own personal benefit rather than their own education, especially when it has a potential to disturb them or their parents and harm the educational relationship of trust.

I don't particularly think there should be JAIL sentences, when I spoke of punishment I meant more along the terms of a pay cut or temporary suspension. At the most, fire him since consequences to teachers are commonly based on how many parents get pissed off (and obviously most parents do get pissed off about this, or else pretend to because they're afraid of speaking otherwise or they'd lose their kid to the mob).