Finding totals withing a seven day period

If I didn?t want to group student scores by date but rather scores in a given seven day period; how would I go about that? What I am looking to do is to evaluate scores every seven days, comparing the total score of the first seven days to the next seven days and so on.

What I would like to end up with is a Week One (first Thursday) with totals column, Week Two (second Thursday) with totals column, Week Three (third Thursday) with totals column and so on. As students move through, this will give me the ability to see if students are making improvements from week to week.

I realize that I could write the expression by date (3/1/12-3/7/12) but I believe that would require me to write out each date and not automatically provide a count of a seven day period. Lastly, I would like that this not require me to write an expression each week, which would require my attention. But rather that it would be something that anyone could go to and either print or view without my attention.

What do you think? Would this be possible?
Thanks in advance for your help!

Tom