What does it explain? As far as facts go, they tested 1,000 13 year olds and then tested them when they were 38, and they weren't as sharp? Wow, I'm shocked. There are a whole lot of variables in an experiment such as this one, and simply who smoked cannabis and who didn't doesn't gage much.
Of the people who tested lower at 38...How many of them finished high school? How many of them went to college? How many of them sought continual education after college? How many of them use(d) mind altering/destructive drugs? How many of them bumped their heads during those twenty some years? lol.
It doesn't explain why 13 year olds can learn a foreign language faster thana 38 year old. It doesn't explain why 13 year olds explain to 38 years olds how to use Internet Explorer, Microsoft Office, or any other basic computer programs. In other words, some smart 13 year old in the seventies is still smarter than his classmate at 38 who dropped out of high school, dropped off of some scaffolding onto his head, and also likes to smoke pot. The entire"research" was two IQ tests. Come on, that is not research or proof of anything. No medical scans of a brain before, during, after, etc.?
There should just be a set age limit for adulthood. If you're old enough to be trusted with a car, then you should be able to defend your life with a handgun, etc. If you're old enough to work a job, you're old enough to come home and unwind from that job in whatever way you prefer. Some people like music, some people like watching the news, some people like to play video games, some people like to drink alcohol, and some people like to smoke cannabis.
Still, it's probably good advice to not let your kids drink or do drugs while they're still in school. I never needed cannabis to have a fun time when I was a teen. Although, someone did mention ADD, I've also read cannabis can help with MS, slowing brain cancer tumor growth, PMS, IBS, depression, etc. So,with anything else, use in moderation and you'll probably be fine. I didn't try it until I was 21, and I made the Dean’s list last semester, and the one before that.
I saw the US paid for these Kiwis to get high for this "study". I wonder if they put any money into researching what cell phones do to a teen’s brain.