There are plenty of students (more than some) in non-gifted classes who genuinely want to learn and work hard. But there are two issues that make those classes

There are plenty of students (more than some) in non-gifted classes who genuinely want to learn and work hard. But there are two issues that make those classes terrible: 1) Teachers dedicate 80% of their instructional time to the 20% worst performers, and every incentive pushes them in that direction. 2) More than that, it only takes one or two kids with behavioral issues to reduce teachers' instructional time from near 100% to near 0%, and there's no way to move them out of regular classrooms to classrooms focused on their needs. So if you're a regular student in a cohort with a couple students with behavioral issues, you're pretty much screwed.