For the most part, schools stopped tracking. In doing so, kids on different levels are placed in the same classes. In those situations, the teacher has to teach to the middle, leaving students on opposite ends out in the cold.
The results of this was/is, that the brightest students don’t get their needs met and tune things out.
The weakest students don’t learn either and end up feeling inadequate.
In both cases, some student get disruptive and in the ends, nobody learns.