One of my friends recently met one of the most intelligent people he's ever known. I have to take him at his word, but it turns out once a year he does meth for 3 days straight and reads a giant stack of about 20 books each time.
I'm not condoning meth, but the military and 50s housewives used to use it and these days most of the people who get fucked up on meth are smoking drano or whatever random chemicals are found in crank, a byproduct of producing meth. The byproduct is much cheaper and has some meth in it, but it's very dirty. This is what is poisoning your average meth addict, not to mention lack of nutrition which could stem from impoverished conditions.
Then you have millions of people probably on adderall, which is amphetamine salts. They perform better in school.
So, I guess my point is, that I'm not going to dismiss the ONLY body of research on a subject due to ad hominem attacks. We know for a fact that the anti-drug (pro-alcohol lobby) has done plenty to discredit themselves on cannabis research, claiming among other things that cannabis kills braincells and reduces intelligence which we now know is hogwash.
Nearly all of our body's regulatory systems are based on cannabinoids, and taking cannabis helps our body's better regulate these activities so it makes sense that ingesting cannabis at reasonable levels, and possibly without ingesting too much THC, could help spur quicker development.