None of his books are about secondary schools.
How Children Learn is really about how children learn in the preschool and early school years. 90% of the book is about children, mainly his own nieces and nephews, and how they react to different situations, how they seem to learn, etc.
The school he taught in, which appears in the book, was not a typical 1950s American school, but a very progressive, small, fee paying school, more similar to the British schools of the 70s (trendy teaching methods, project work, etc ;-0 ), or a proper Small School. So his criticsms are of a learning situation in a school that most of us would see as a pretty good one.
As I have said, only his first two books are really about schools at all anyway.
But we have had this debate many many times now. Could we reduce it to specifics? Which books of his have you read? What is it specifically that you object to in his books? Is it that they were written a long time ago? That won't really wash. A lot of helpful things were said and written 50 , or even more, years ago. The human condition has not changed THAT much in half a century, and kids are still, IMO, fundementally the same, imo. We al just seem to go round and round in circles here.
OP, I'd give Holt a go. I mean, WHAT do you have to lose here? He's pretty easy to read. At the least you'll form an opinion on him. But as I say, his later books are more relevant IMO. The only reason for the earlier ones being better known is that they sometimes appear