http://www.boarddocs.com/vsba/fairfax/Board.nsf/legacy-content/867SLA2A9049/$FILE/R3205.pdf
It is recognized that students vary significantly in the amount of time they need to
complete given assignments. Teachers should estimate the amount of time the
average student would require to complete an assignment. In general, homework
across disciplines should not exceed 0.5 hour in kindergarten through grade three,
1 hour in grades four through six, 1.5 hours at the middle school level, and 2 hours
at the high school level. Long-term projects may require additional time. Teachers
should adjust daily homework assignments accordingly.