I don't let my mind wander. My mind runs off on its own without ever asking permission. I am sometimes able to get it to sit still long enough to write a History test and it usually obliges me when I have something important to do, but the most of the time it is off someplace, far out of cell phone range.
I think it just gets bored most of the time. When I'm in an interesting discussion in Ethics class or in rehearsal for the next show it will usually stick around, if just to see what will happen next. But in a long Economics lecture going over the same thing that was said in the reading the night before my mind just gives up.
It's just lucky that my brain is willing to fill in. Maybe that's why I do so well in Economics and Physics. My brain just sits there, storing up the rules and principles and not asking all the difficult questions that my mind would, like, "if we have to assume all that, doesn't it mean that this will never actually be applicable to real life?" The answer to that one is invariably, "you have to understand this highly oversimplified model, almost completely worthless in any context except the final exam, before you are considered worthy of any knowledge that might actually be useful." I've stopped asking now. Instead I just go online, read about the theories that are at least somewhat relevant to reality and figure them out myself. Usually my mind joins in and it can even be fun. General Relativity and non-real numbers are quite entertaining, if only because they require leaps of understanding, not rote memorization.
Trying to follow my mind while it considers a problem or theory takes super-human effort. It will somehow go beyond logic or rationality and comes up with the answers without having the slightest idea itself how it got there. My brain always has problems with this approach and will end up trying to second guess my mind resulting in massive headaches from the bickering if I don't step in at once and stop the argument before it gets going.
Recently, I have managed to get my mind to do some thinking within accepted modes of thought, but it's difficult. Much simpler is just sitting there and watching my mind work backwards. It has to go slower in reverse and I can usually follow along. Occasionally I can even force my mind and brain to work together, which is when I do all my best work. The rest of the time, it's either logical or interesting, but almost never both. Hopefully, when I can finally get through all the oversimplified models and start learning about all the really interesting stuff, my mind start asking permission before it takes off. In the meantime, I'd better go, my minds off playing with worm holes again. Yes, I know, but even if we were able to perceive seven dimensions, it still doesn't solve the problem of their basic instability.