This past week I taught equivalent fractions.  As an activating strategy (after previous lessons on equivalent fractions) I created four posters with a different fraction at the top of each poster.  Each group had to use a different color crayon (which we identified before the lesson started).  The groups had one minute to write as many equivalent fractions that they could on the poster.  After the minute the students stopped and put down their crayons.  I rotated the posters around to the different groups.  The students were not allowed to repeat any fractions that were previously written. I encouraged the students to whisper to their group members so they weren't giving away any strategies.  The students LOVED this activity! They were actively engaged and enjoyed the competition!