if your boy wants to get back into bmx racing, he will be spoilt for choice of tracks, there are 5 good race tracks in the metro area, and if you live at Flagstaff, you will be 10/15 mins drive from 2 of them. Where is the bmx track in Flagstaff? trying to think , but really can't picture it. Regarding skate parks, there are a good number around, off the top of my head, near to Flagstaff Hill there are - blackwood, manning road (aberfoyle park), Brighton Road, West Beach and a smaller one at Hallet Cove. Dirt jumps are everywhere.
to JDHogg77 Re Wirreanda, I don't think that school has a fab rep either, however, I know someone who has a child there and has no complaints, but I also know a teacher there who would not send her son there. As you say, you need to look round them all.