Sam Blumenfeld gave this lecture at a Texas homeschool convention in the 1980s where he explains how the “progressive educators” conspired to dumb down the children of America: https://www.podomatic.com/podcasts/shurtleffhal/episodes/2022-01-10T17_32_34-08_00
This presentation as well as most of the work of Sam Blumenfeld can be found on the Blumenfeld Archives: https://campconstitution.net/sam-blumenfeld-archive/