Sorry, beatback - what are you on about? Where do you get the year 1946 from? Late 1945 and then 47 are the key years.
I would argue that the Attlee Labour Government was committed to Secondary Moderns, but the first Minister for Education, Ellen Wilkinson, was committed to Grammar schools because she had done well out of the system. I would certainly see it as a lack of vision on their behalf.
By the 1960s the system of Secondary Moderns was loathed by a good many,(even though there were some good secondary moderns), because children felt that they had been labelled as failures.
I suspect that in the 1960s an alternative could have been to implement a real push to build the missing technical schools that a lot more would have been satisfied - they would have taken the 60% of children in the middle. My SIL was one of the few to go to one, and she was perfectly happy there. She knew the academic curriculum of the grammar school wasn't for her. Sadly the family moved house when she was 14 and the new town only had secondary moderns, not technical schools, which was where she had to go to. I don't think she ever fulfilled her potential as a result.
Then, as now, there is no real attempt to value technical education, despite a number of good proposals being put forward over the years.