I have not worked during nursing school, but several (3 or 4) of my classmates have worked as CNAs and have managed to do well. Clinicals seemed to be easier for them because most of what we do is CNA work in the first three quarters of clinicals (besides giving meds).
The course is very demanding. Most of the classroom work is similar to what we have already learned in anatomy & physiology, but more nursing centered. You are required to memorize all the meds you will be giving to your patients (how they work, side effects, etc.) during second quarter, as well as to create nursing care plans that must be okayed by your clinical instructor. Second quarter was probably the most difficult because of this--it was so time consuming. Final classroom test grades must be 75 or above or you will flunk. Just be ready to be totally committed and to live, eat, breathe nursing! You can do it.