This page is part of the Teachers Helping Teachers site and includes the top ten most requested middle school math lesson plans. Scroll down to find a lesson that might work for you. This site is called the Middle School Math Problem of the Week.
Students solve the problem posted weekly and submit answers online.
This could be a weekly Internet incentive activity for students. This problem of the week site works just like the Math Problem of the Week site above. Students submit answers online. On this site, students can submit problems and explain their confusion and attempts at solving the problem. They must show their work and explain why they are stumped.