The theory I currently most subscribe to is that school does in fact act as a economic signal more than impart significant value. In almost every case, IQ is still a better predictor of ability. The difference is that J correlates well with certain ethics - work ethic to written corporate ethics. In short, more discipline = better marks = signal for good work ethic. It was only recently that I realised that this is probably true regardless of discipline (I would put research and theoretical aside) after meeting both educated engineers and pratically taught engineers - I was unable to sort them out at all by education level. For all intents and purposes they were the same... and natural intelligence didn't seem to correlate at all. Some were from poorer countries and didn't get a chance (and surely would of gone otherwise) while some chose not to go. They still needed liscences to work with machinery, so there were barriers of entry that may of required some basic learning - I'm unsure if they took classes just for that.