Good idea, Ellie.the, "I tried my best..." explanation always kills me. (Sorry, not trying to advertise but I don't know how to give this to you any other way.) If you'd like, stop over at my store (Pamela Kranz) and grab my free Become a Math Lawyer, Defend Your Answer poster/label set. It broke my 6th graders of the I-don't-know-but-it-looks-right routine. :) Good luck!
Thanks, Pam, I'll check it out!
My students always mix up the rules with decimals/fractions/integers operations. It is important to teach them the reasons why instead of just the rules. Like you said, they need number sense. When you add decimals, you are adding place values. When you multiply 2.7 x 2.4, you are making 2.7 groups of 2.4 and estimating helps determine your answer. Interesting way to put this! I've got a year to rethink my decimal operations unit.
<div align="center"><a href="http://ellienix.blogspot.com/" title="Middle School Math