I just read my letter now, and I really want to go! I can't choose between Boston or D.C... location shows you exposure to different places... Johns Hopkins and the White House, or Harvard and Tufts? Gah! Someone help ):

I had the exact same problem; same locations. my brother had gone to Boston 2 years before me, &his friend had gone to D.C. the year before me. I talked to my brother &he really liked Boston, but when I talked to his friend he told me that I had to go to D.C.. he told me that he had absolutely loved it &that I just ahd to go there. so I decided on D.C. because I liked Georgetown. now I'm glad that I did. I can't really give you a reason why--I think it's mostly because of Georgetown (I absolutely love it there!).
Besides, if you go to Boston, there's no guarantee that you'll go to Harvard or Tufts. I mean there's no guarantee for Johns Hopkins either, but you can definitely count on seeing the White House!

DC all the way!!!!!!!! I went to DC last year and it was pretty awesome, I couldn't decide between DC and Boston, but DC just ended up working out better for me cause I had family I could stay with and I missed a week of school. I completely recommend DC!! there are some really awesome places to visit

Were there mostly high school seniors participating or are there juniors and sophomores as well?

when I went, it was the summer before my junior year &it was that way for a lot of people. there were quite a few going to be seniors, &a couple going to be sophomores. I even had one kid in my group who had just graduated &was going to college. so age kind of varies.