I remember my parents trying to get me into advanced classes in sixth grade but the school rules said it needed to be done by third grade. I couldn't skip a year either, it was too late.
The second (harder) way into double advanced classes was to pass a test going into high school. That test contained math that only those already in advanced classes had been taught. I aced the reading portion, scoring at 11th grade reading level, but it wasn't enough.
The same year I was sponsored to be an exchange student to Europe but my family couldn't afford the plane tickets. A year later, bored out of my skull and disappointed, I gave up completely on public school.
I embraced mediocrity because I figured out I could get by with no real effort. I concentrated my creativity outside of school and learned more programming languages and electronics. I never got above a C average again until college.
Some teachers saw promise but I let them down because I didn't show up to class and was always in trouble. I knew I had missed the boat to the good classes that led to good scholarships and onto good colleges, and I was bitter and didn't give a shit anymore. To get into the caliber of school I dreamed about I would have needed more than just good grades in regular classes, and all the windows except sports closed before highschool even started.
There's been some articles about "lost diamonds", which may explain why smart people do better as a whole but the large majority still end up living average lives and doing nothing of note. I might not have been any smarter than average, but I definitely feel like I was one of those kids who the system left behind. I knew many others I considered smart that shared my company at the troublemaking fringe of highschool society, definitely a pile of wasted potential at the bottom.