So, here is my take on command - it either comes or it doesn't. I don't teach command; I teach consistency and velocity. In my experience, command comes with repetition once mechanics are cemented to the greatest degree possible. The more you screw around with mechanics, the longer it's going to take to maximize command. I used to try and teach command by targeting and focus - trying to pitch to smaller and smaller spots. Others try to get command out of their pitchers by tempering velocity. I really don't think either method works. In the past few years, as I continually increase my focus on underweight/overweight programs, I believe I'm seeing much better results in improved command that accompanies increased velocity. I think a lot of this has to do with proprioception work.
My best example is always Randy Johnson. You may remember that early in his career, he was about as wild as it gets in the majors. He was also constantly screwing around with his mechanics. Once he got that down, his accuracy greatly improved.