We just finished our second week of school, and I've rated my class (and myself) at the end of both weeks. I created an Excel spreadsheet with an extremely simple averaging formula. Each week has a column and each kid a row. I put the kid's rating for the week in the appropriate cell and it does all the work for me. My class went from a 2.66 to a 3 in a week.

I probably rated them too harshly the first week, but that's okay with me.
My own score dropped from an average of 9 to an averaged of 8. There's this one kid who's just
really irritating me...so, it's up to me to monitor myself and lead him into the realm of perfection.