A true diversion plan (PTD) involves no plea at all, and a Nolle Prosequi from the state once the plan has been completed. While this should have certainly been the case here, It wasn't, and your son was led into accepting a plea. If you are still within the proper time constraints, there is a much nicer shortcut to the expunction process that applies specifically to juveniles who have completed juvenile "diversion." it is linked here: http://www.fdle.state.fl.us/Content/...Diversion.aspx
This is a totally raw deal, so good luck and let me know if I can help.