For the cover I started with a flexible cutting mat I bought for $1.
Cut two 3x5 pieces with a rotary trimmer and sand the edges so they aren't sharp.
Punch holes in the corner.
Cut a weird creature (also 3x5) out of a gaming magazine (you can use something cuter if you'd like, of course) and laminate it with clear wide packing tape to make it sturdier. Also punch a hole in the corner.
Download the 3x5 homework planner template (pdf) and print it onto cardstock (there are four cards per page, print enough so you have one card for each class). Cut into 3x5 cards and punch holes in the corners. Note: your printer may shift the template slightly, but you should be able to cut 3" and 6" strips starting from the top left and then cut those strips into 5" sections.
Make a stack with the front cover, magazine image, 3x5 planner pages, and back cover. Bind it together with a quick link or something else from the hardware store (not anything girly from the craft store).
And here are the simple instructions to use the homework planner: Write a class at the top of each card and keep track of assignments and due dates for that class. Cross off assignments when you turn them in. Add a new card when the old one is filled up. Remember to take it to school. :o)