We just moved back to PA after 5 years in NC. One thing I was NOT thrilled about was the HS laws, which I was well aware of before the move. On the bright side, we have a while until we need to report (DS is 6), but yeah, I'm not fond of the laws here. In Philly proper it is tougher with the mandatory attendance being age 6 vs. 8 elsewhere in the state.
It seems like the laws here are workable but you really just need to be familiar with the law. Find an USing friendly evaluator (HS support groups online and IRL can help you wit this). I believe test scores alone aren't enough for them to compel you to put your child in school...the wording is something like sustained progress in the "overall program" must be made. Pretty tough for them to prove that isn't happening.
But yeah, I feel for you. I'm hoping we can keep advocating and moving forward and working on getting things changed here in the years to come.
It seems like Philadelphia's school system has been making some potentially extra-legal requests in recent years (was reading they were sending out letters this year about having to hand in the ports a certain week in June, not just by the end of June, and the letter mentioned meeting w/ the superint. which seems kinda questionable from a legal standpoint. I'm hoping that gets challenged from a legal standpoint.
If you could do Jersey (but still near Philadelphia) things would be much easier as an USer, but then you have the issue of taxes, etc. often being higher IME.
eta: have you checked out the askpauline site? Google that for some great tips on HSing in PA. There are also several yahoo groups (including one for USing in PA) if you aren't aware of that already.