In my opinion, students shouldn't have a job while studying, because a job prevents studying.
If student has a job while studying, he has no time to do homework or prepare to lessons. But some students have no money for living and they cannot study without a job. In my opinion, if you have no money for studying at one university, you need to go to cheaper one and study there. If student has a job while studying and he is preparing for all lessons, he has no free time and enought time to sleep. They can live so about few months, but because of sleeplessness he will be ill all time or very tired and won't be in a condition for studying.
If I was a student, I wouldn't have a job while studying because I like spending my free time for reading books or playing a computer.