We've heard:

- It can make kids "overconfident when they see material they think they already know, so they end up not engaging."

- Some programs, particularly RSM, are criticized for valuing speed over depth. Current culture for K-8 math teachers is the opposite, they value depth over speed.

Left unsaid:

- It can make the teacher's job harder when the class has a wide span of abilities.

- Current teaching culture is skeptical of accelerating and/or skipping grades in math.

Notably, we've never heard English teachers be upset about a kid reading a book outside of school that's above grade level, or using advanced vocabulary in an essay. They tend to praise it.