What I did:  We were starting a unit on functions and our book had this neat activity about making a function machine.  I gave the students 2 note cards, and the page number to find the instructions.  We did the activity on a day when some students were finishing up other things, so all of the students were working on this activity independently throughout the class period. 

The Function Machine Activity:  Students cut out a small box on the left and on the right side of a note card.  They were to hold the card vertically while doing this and also were to leave some space in between the two boxes.  The left box was entitled “input” and the right box was “output.”  The middle was entitled “rule”.  The second note card was to be lined up vertically exactly behind the function machine note card.  This was done to determine where the left column of numbers was to be written so that the numbers would show through the input hole.  Then the students were instructed to list the numbers from -5 to +5 down the left column.  They were to then fill in the rule [which was “multiply by 3 and add 2”] for this example. 
Next they were to line up the function machine with the list of numbers and then slide the function machine over the list of numbers.  As each input number showed up in the input window, the students had to follow the rule and fill in the output number in the output box [which then made a column on the right hand side of the second note card].
This activity was followed by some questions expanding the idea of a function and how it relates to an equation.  The activity ended with the students making a second function machine [their own example and input choices] and letting another student fill in the output column.     

What the students learned:  I see, as I am looking over some of their “function machines” that they pretty much followed directions and seemed to understand how the machine worked to get the out put column.  However, there were some expansion questions with the activity about changing the rules to equations.  This did not go as well.  I am seeing that they understood how to get the rule, but didn’t write it in the proper form.