My experience has been that it is a benefit for part-time and full-time employees, and that they will allot you a certain amount, either per semester or per calendar year. You usually have to sign an agreement to stay with that company for at least a year in the same status that you currently work, part-time or full-time, or you will be responsible for paying it back. Also, there is generally a set amount that your employer will pay. If your tuition is $10,000/year of school, your employer may only pay half of that amount and the rest is up to you. I doubt if many employers just write a check for the full amount, that would be outrageously expensive. And, you don't get it until you finish the semester and get your grades, so you may still have to get a student loan and then use the tuition reimbursement to pay it back later, since tuition is normally due at the beginning of the semester.
The hospital system that I worked at until recently offered $1,500/calendar year for part-time employees and $3,000/calendar year for full-time employees, payable after classes are completed. That amount would not normally cover a full year of school in most places, but, as one co-worker pointed out, it's a lot better than nothing and in most professions you don't get tuition reimbursement at all if you choose to further your education.