I think it's a lesson in reasoning for the kid with regards to drawing boundaries. The boundaries might deal with what is considered acceptable behavior in a classroom. Things like behavior which might be considered mischievous and such are addressed.
I suggest talking to the school on what that threshold is.
Personally, I have seen teachers using time-out by singling out the misbehaved ones and isolating him/her from the class activities temporarily. He/she is never left alone indefinitely. After several minutes, the teacher tries to reason with the kid regarding the offensive behavior and invites that kid back in with a proviso that such behaviors (or even lack of it) are not to be revisited.