I just take something small and uncomplicated with me everywhere and get in a row or two. I have a practice skein for learning new bits--working on cables at the moment--I get practice in, and I don't feel frustrated if I mess up.
Another way to work it in when busy is to think of it as a treat. Like right now, I am grading essays, and this morning I've been grading a couple (for 30 or so minutes), then "treating" myself to a few rows of knitting. That way I don't think about how I wish I were knitting...I use it as a reward for getting my work done
So, after you read a chapter, or do some math problems, whatever it is you're doing for homework, give yourself a treat for being a good student: knit! It even helps get the brain going, all that creativity!