Okay, reading some more stuff from the blog, my impression improved. He seems to be a great teacher (example 1, example 2). It's just the IQ hypothesis that I disagree with, but I guess for many readers that one is the most interesting. I am tempted to propose a compromise hypothesis, that at the lower end of the IQ scale IQ is the hard limit of ability to learn, but at the higher end of the IQ scale the most limiting factors are elsewhere.

Some quotes I liked:

It’s the delusion of eduformers and progressives, one and all, that if teachers find the right approach, a low ability kid is transformed into a competent high ability kid.

Sure, magic skills are a requirement for a teacher. On the higher end of the IQ scale, the delusion is that a spoiled kid with behavioral problems who never had to work or behave at school and right now is acting even worse than usual because their parents are divorcing... can be transformed into a hard-working and well-socialized student by saying the right magic words.

I am a teacher who doesn’t overvalue any individual student at the expense of the class, which means I have no compunction about kicking kids out for the day. You run into these teachers philosophically opposed to removing kids from class; how can these students learn if they aren’t in class, they bleat. These teachers never seem to worry about how all the other kids learn with a disruptive hellion wreaking havoc because, they strongly hint (or outright assert), the right curriculum and caring teachers would eliminate the need to disrupt.

(Source.) This reminds me of "The Naughty Boy" and "The Disruptive Girl" from Scenes from the Battleground. The difference on the higher end of the IQ scale is that each of those misbehaving kids is a certified special snowflake, and their parents often have good lawyers or sponsor the school or both, so you just can't kick those kids out of the classroom when you need to.