You are probably already too late to sue the school. Your state's statute of limitations began running when the incident occured. See a lawyer ASAP to see if there's a valid exception to the statute of limitations.

--to the original question, the SOL is way down the road. Just keep your fingers crossed. The longer the delay to charge you the stronger the argument that it was a minor offense. Just be sure that they did not charge you. It's possible you are in default on the case.