I have a number of comments.
As to Lockhart, I read only the first page and have to take issue with his suggestion (by analogy) that no mathematician was involved in the new math. Many were, I regret to say. But the real problem with the new math, was the teachers had no idea what they were doing and trying to do it by rote. Two stories:
My daughter in fifth grade was given the problem of counting the number of subsets of a three element set. “Express your answer as a power of 2.” She gave the obvious answer 2^3. “No, the teacher said, it is 256”. She had misunderstood the instruction and calculated 2^8. That is almost more a problem of English than math.
My son in fourth grade was being taught base 6 arithmetic. The teacher had a bunch of examples like 35, 34, 15, 28, and then 61. She had discovered for the first several (all less than 36) that you divide by 6 and use the remainder as the first digit and the quotient as the second. So 35 is 55 and 34 is 54, 28 is 44 and so on. For the last one, she applied her algorithm and got 101. “No”, my son insisted, “It is 141”. “Why do you say that”, he was asked. He answered that he had learned how to do base 6 arithmetic the previous year (when I had been on sabbatical) in Switzerland. Her answer was classic. “Maybe that’s the way they do it in Switzerland, but this is how we do it here.”
I don’t recall learning addition, but I learned multiplication in fourth grade. We were not tasked with learning the multiplication table. There was a large multiplication table on the wall of the classroom and were regularly given multiplication problems, using the table on the wall. By the end of the year we had all memorized it faute de mieux. Not only that, but I at least had absorbed things like the regularity of the 9 times table (in each row, the tens digit went up by 1 and the unit digits went down by 1) and also that the 8 times table was similar (if you ignored the singularity at 5 * 8) and so on. I have never come on another person who learned it that way.
I had a 7th and 8th grade teacher who gave us make-work homework, which I hated and never did. But even she couldn’t stop me from having perfect tests, although she never gave me an A. She didn’t quite succeed in killing the subject for me, although she tried hard.
Of all the replies I have read two really seem right to me. First the general incompetence in math of elementary teachers, and second the ignorance (not “ignorant”) culture that automatically distrusts anyone who knows anything.