Who knows? Maybe they are waiting for something in the investigation? Is Monday your arraignment? If so, they may amend the charges then.

If you were caught with dealer level quantities on school grounds, you can be charged with possession with intent (or it's Michigan equivalent) and any pertinent school zone enhancements.

You may have served 5 days suspension for now but if the charges are upped or you are convicted, the school may move to expel you.