Hi, poolboy!
You can use Data tab, Data Tools group, Remove Duplicates button.
Asuming your data is in A and B columns, just select them, press the related button, et voila! No more duplicates.
Then in C1 type =COUNT(B:B) for first question.
For the second question, from D1 down type all the class years, and in E1 type =COUNTIF(B:B,D1) and copy down as needed.
If you want to preserve the original A&B columns, just copy them before to C&D, and adjust the two formulas.
Regards!