I'd rather skip a middle four. It's necessary for everyone to learn basic things like literacy and arithmetic, but remember that the idea of setting school leaving age at 18 was supposed to be that you would then have finished your education. If most people are going to be going to college, then school leaving age should be set at 14, so that you can spend those next four years learning something useful instead of just marking time while you memorize the dates of Napoleon's battles and the agricultural products of Denmark.