The other problem is finding employers that will respect your class schedule. My first two attempts at working my way through college ended with sudden work schedule changes early in the semester, and "work it or get fired" orders. Both times I quit the job and finished the semester on ramen noodles and the generosity of friends, then had to take other jobs that were completely incompatible with any available class schedule.
Or profs who will respect your work schedule...
I had to drop and retake a calculus class because the prof was an inflexible
. Class was at 10 AM, exam section was at 4pm, I worked in the facotry from 3-11 every night. After the first day of class when the syllabus was handed out, I talked to the prof and told him of my situation and asked if I could take the exams earlier in the day, he said "no problem, we'll work something out when the time comes."
A week before the 1st exam, I approached him and he told me "No. I do not schedule special tiems for students who can't make it, either show up or drop my class."
This was back in 1993 or so, and I was getting $10.50/hr for 40-45 hrs a week... I wasn't going to drop the job for a $500 class.