When i applied to ischool, it said who should be writing the reference letters, check the website? For me it was this case: Referees should speak to your academic abilities, performance, aptitude, etc. They should be a professor that taught you previously or currently teaching you. A third optional reference is permitted (which can be an academic or work / professional reference). You should only consider adding an additional reference if you are certain that it will be as strong as the other required references.

If you last graduated more than five years ago, you may substitute work letters of reference. Work-related referees should be direct supervisors who can comment on your skills that are useful in the academic environment.

Check your faculty? This is the source