Ahh, right!  I was thinking longer term.  For example, the IQ of our species, or the species that developed into our species, was lower before oily fish entered the diet.

IQ is not a very accurate measure of likely academic achievement anyway.  My original point was if you broaden the curriculum without increasing the time spent on it, you will inevitably dumb down cos today's children have the same intellectual capacity (in general terms) as their parents and grandparents, given evolution works over a much longer period than a couple of generations.