Big hugs m2gts. Defiance is tough and we've had a fair dose of it in my household. We've tried lots of different things with varying results (magic 1-2-3, sticker charts, pocket money, homeopathy, etc.)
For me, fostering intrinsic motivation has been the answer. When Miss 7 is motivated to do something (at the moment it's spelling), then she just gets on a roll and her overall behaviour at school improves. Working out how to develop intrinsic motivation is, of course, pretty bloomin' tricky. But for me the key question is... where's the blockage coming from? What's the pay-off for your DS of being defiant? What's he getting out of it? And how do you foster good learning behaviours for use at school and home?
Few answers, but lots of empathy... jojo