Pros
You get to know the kids and families throughout the years (I was there 3 years and had the same kids and their siblings). I was promoted from an aid staff to a professional staff sub pretty quickly (Started in January, was gone from May - August because I was a student and was promoted in October) and the increased responsibility and minor increase in pay were great.
Cons
None, as long as you like being on your feet and working with kids!