Some of you responders seem like real jerks.
OP, here are a few links to other similar research, all available from Google Scholar. If you vary your search terms, I suspect you can find lots of data that will help you.
http://scholar.google.com/scholar?hl=en&q=change+in+homework+over+time+decade&btnG=&as_sdt=1%2C11&as_sdtp=
http://hss.cmu.edu/history/docs/schlossman/A-Nation-at-Rest.pdf
"We use several national surveys to provide a 50-year perspective on time spent on homework."
http://files.eric.ed.gov/fulltext/ED383498.pdf
"This book investigates teaching practices before, during, and after reform impulses in the 20th century aimed at changing what teachers routinely do. Paterns of stability and change over a 90-year period are developed from evidence from a wide variety of sources, including clasrom photographs, textboks and tests used, student recolections, teacher reports of how they taught, and clasrom observations by parents and administrators."