"Lately, I've been taking off my shoes as I walk to class, but my feet are starting to feel a little tender already."

You're on the right path. Just need to listen to your body. When I feel like that I put my feet in minimalist shoes 'till I feel like I can try barefooting again.

The good news is that "forever being a "barefoot in the house" kind of girl, and recently going barefoot much more often" should help you a lot with the transition.

You don't need to develop callouses to become less sensitive. Callouses are a result of friction. If you have a smooth gait with straight up and down movement you shouldn't get any callouses barefoot. You will develop more muscle and fat tissue to pad your bones. Flexible soft skin with a nice fat pad underneath can bend around obstructions instead of creating painful pressure points. A part of the adaptation is also in the brain, as it gets used to the torrent of signals from the feet, it slowly learns to sort them better and stop flagging so many things as unexpected and possibly dangerous (aka painful).

Very interesting! I've always had very soft feet, and while they do blister sometimes (usually as a response to barefooting on HOT rather than rough surfaces), they never really get callouses. My mom has elephant-style callouses on her feet, and she always assumes that mine are the same- always seeming surprised when she realizes that my feet are almost as soft as my hands.

So what does it take for this muscle and fat pad to develop? I wonder if I already have a decent one. I've stepped on rocks, nails, glass (larger chunks, not sharp shards- I avoid those), etc without hurting myself at all. Perhaps it's the brain sensitivity that needs to "build up" each year rather than the physical padding.

(I am a biology/psychology double major in college; this conversation is right up my ally- both of them, haha!)