The last year. Senior year is a milestone--why not commemorate it? It's also a way for parents to keep their children close, even when they leave to go experience the world and "grow up".
Most senior packages are a flat $300. This includes all-digital copies of every picture you like and 6-8 hours of photoshop work. This way you can also order as many prints as you want and not pay a high cost. I also work with the customer--you can tell me if you want a specific special effect on any given picture, and I will make it happen.