Ken,
I don't know enough about working with the questionnaire for this, but if it was me, I would use a database, with all the possible exercises as separate fields(if there are not lots and lots of different kinds). Then each week students would add a new entry with their work for the week. Teacher can download each week and either keep all previous data or easily delete previous data and only keep that weeks work.
Perhaps someone else knows more about the questionnaire.