There may be a mechanism to explain the cases of autism that improve with organic food. It is speculative, but all the major pieces are there. It has long been known that conditions in the intestine affect the immune system. This makes sense since the intestine is essentially the headquarters of the immune system. New research shows that the immune system modulates brain functions that determine perceptions and behavior, at least in mice. It is a fair guess, then, that certain agricultural chemicals in food could have an impact on the immune system that would lead to decreased levels of certain brain functions. If so, removing the chemical load by eating organic food would tend to restore those same brain functions. Obviously, a lot of details are missing here, but the discoveries lend credence to the anecdotes about autism improving with organic food, elevating it from the level of anything-is-possible to might-be-worth-a-try.
Another intriguing result of the recent research is the thought that autism and schizophrenia could have some mechanisms in common. One theory briefly considered historically was that the agricultural chemical DDT was the cause of schizophrenia. No convincing mechanism was ever found, but the incidence of schizophrenia dropped at the same time that DDT was phased out. Of course, there were other chemicals that were used and abandoned in the same historical period, so the culprit could just as easily be another chemical rather than DDT. It may be time to take a new look at all diseases of brain function now that the immune system is a confirmed part of the brain function puzzle.