I would counter-counter that there practically no teacher that can teach. Elementary & high school math teachers deliver a lot of practice, but that ultimately they really just aim to "teach" the kids who naturally understand math. The rest just stumble along and the system covers it up. The same is true for English, History, Phys Ed and pretty much everything.
I don't think the same is true for everything, but I do think this is the case in a fair bit of Math classrooms. I've tutored both a friend (same age) and his his younger sister (5 years younger) and they both struggled with the same exact concepts. Granted, you could say it was genetics, but after some creative examples, they were able to better their skills. It looked to me as a direct failure to truly "teach" Math in the 6-7th grade level of their elementary school district.
