Barry Garelick, via a kind email:

I am a mathematics teacher. I majored in math and, prior to going into teaching, used it throughout my career.
My facility with math is due to good teaching and good textbooks. I fully expected the same for my daughter, but after seeing what passed for mathematics in her elementary school, I became increasingly distressed over how math is currently taught in many schools.
Optimistically believing that I could make a difference in at least a few students’ lives, I decided that after I retired, I would teach high school math. To obtain the necessary credential, I enrolled in George Mason University Graduate School for Education in the fall of 2005.
The ed school experience did have some redeeming features. Most of my teachers had taught in K-12, and had valuable advice about classroom management problems and some good common-sense approaches to teaching that didn’t rely on nausea-inducing theories.
Those theories are inescapable, unfortunately.
Specifically, many education theorists hold that when students discover material for themselves, they learn it more deeply than when it is taught directly. In this vein, the prevailing belief in the education establishment is that although direct instruction is effective in helping students learn and use algorithms and mathematical procedures, it is ineffective in helping students develop mathematical thinking.