Not defiant so much as merely independently-minded. There were some classes where I knew the material better than the teachers, and some teachers that were such pricks/cunts that I would tune them out completely.
Unlike @stranger_in_a_strange_land, I never broke rules intentionally; I merely lived by my own rules and occasionally my rules were different than the school’s.
I settled down considerably in the 9th grade since most of my fellow students got bored with picking on me and the teachers had advanced warning. (The 37 times I got in-school suspension for fighting in the 7th and 8th grades also played a role.) However, I did require a little accommodation and am glad that my HS teachers were open-minded and had a sense of humor; I’ve always been a bit of a smart-ass.
In computer class, I never did the assigned work, but I passed with a B+ since I demonstrated that I knew more than was being taught. Same thing with “Our World Today”, a current event Social Studies class.
Part of it also may be that I realized that there are more important things in life than making others happy or academic excellence; life isn’t worthwhile if you scramble around serving other’s whims. Once I realized that life was more enjoyable when I lived for me and my loved ones rather than for others who barely/don’t really care about/for me, all became better.