Pros
The kids are always great. If you like working with kids, you'll enjoy working at Mathnasium. The schedule is often flexible. I personally tried to work as many shifts as possible but I know we often had people on the team only working one or two shifts a week by choice.
Cons
Not enough hours to make a living - you need to find another part-time job to fit around the centre's hours if you are trying to support yourself. The schedule through the school year is kind of annoying if you work every day it's open. You work Monday-Thursday, have Friday off, then work Saturday, then have Sunday off. It might surprise you how much different having two days off in a row vs. two separate days off can feel for your mental health. I found both centres I've worked at to be somewhat unorganized and often the communication with staff about things like schedule changes, summer hours, etc. was delayed or nonexistent.