https://www.intellectualtakeout.org/blog/new-study-suggests-high-school-curriculum-dumbed-down/
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One of the easiest explanations for this phenomenon is that AP courses have been “dumbed down” so that more students can handle them.
This is, of course, true. We continue to recommend The Deliberate Dumbing Down of America, which can be found here: http://deliberatedumbingdown.com/ddd/deliberate-dumbing-down/