If he is in fact "in the system", he should appear on the website at
http://sexoffenders.oregon.gov/. If he failed to register as required, he'll be shown as "absconded/fail to register". How long he must register for depends on his sentence, as well as if registration was actually required of him.

If he's listed, RUN, don't walk, to school officials and yell and scream until somone listens and inform them that they have potentially retained the services of a RSO.