Rewards and Challenges

I think the most rewarding and most challenging would be the same - to be able to guide a student through all 4 years of high school and then to see that student make it to graduation.
I have not completed my interview yet but it appears to me that in my school students fall into 2 general groups - those who require small amounts of attention and those that require large and constant amounts. It reminds me of the 80/20 rule where 20% of the students occupy 80% of your time.
My guess is that they become very invested in the 20% and really feel like they have achieved something when they see that student graduate.