I agree with the others, definitely when they are school its important to start getting things looked at ,even if it just sets a baseline or a beginning level of where he is at.

Id also suggest toilet timing him, so he goes regularly whether or not he thinks he has to go, this may ere net the accidents as he's going regularly anyway. The school might find it frustrating, but push the issue to get them to help and ensure he goes regularly enough to prevent the issues. The school may be able to access a psychologist to help with planning that strategy if needed.

Good luck!