This problem eventually goes away as people are sorted into classes based on their achievement.
It is caused because schools are a "melting pot" for people from various social strata, personalities and intellectual levels.
As people go through life, they tend to segregate and associate with similar people.So bullying based on intelligence diminishes or goes away entirely. I mean, you're not going to be bullied by your peers for being smart if you're a grad student in engineering physics.
The fix is to identify the talented and smart kids as early as possible and whisk them off to separate schools, where they not only benefit from being away from the bullies, but also benefit from a more advanced, accelerated curriculum.