Set up a "homework options" chart. Maybe put a weekday at the top of each column, allow them to choose from that column. Staple to the top of all completed hw on Friday, with their choice for each night colored in/signed.
Here's a FREE Speller's Choice Menu that can be used with any spelling list. The kids love it because there's a variety of activities to choose from, and teachers love it because these activities manage to incorporate phonics, grammar, writing AND math!!! :) I just place it in a sheet protector in their take-home binder for them to use with homework every night.