It was well known in the ‘60s and studies were done on it even earlier than that! The problem is, today, almost EVERYONE can be places on an “AUTISM SPECTRUM” because they ballooned the categories to such an extent, that that term is now pretty meaningless.
It ranges all the way from hyperactivity on the low end to what used to be called mental retardation on the high end.
Schools "ballooned the categories" because parents can collect money for 'disabled' children - and so can the schools..