Contra many responses I think teachers are generally smarter than average by about 1 standard deviation. So smarter than like 84% of their students. The problem is bureaucratic mindsets created by test culture, not smarts.
Teachers have been seen to, by the state.
Modern teachers have almost no autonomy on curriculum, textbooks to use, or even the order in which to teach things
The "good teacher" archetype almost always is a teacher who goes beyond the curriculum / has somewhat of a rebel streak
No, I think it's smarts.
US teachers are around at the bottom of the college-educated population in intelligence, so maybe more like 60th-75th percentile. And I think that's low enough for lack of basic arithmetic skills.