One of my favorite lessons to teach comes from comes from Marilyn Burns’ Lessons for Algebraic Thinking, Grades K-2.  This lesson is called Two of Everything.  While this lesson is very wordy to read, as are most of Marilyn Burns’ books, the heart this lesson is very valuable.  In this lesson the teacher reads to the students the book called Two of Everything by Lily Toy Hong which is about a couple that drops items into a magic pot and they double (excellent book).  This book provides an solid foundation for students to conceptually understand input/output tables because items are being put into a magic pot (input) and items are being taken out of (output) a magic pot.  Then students create their own magic pot patterns on their own input/output charts.  When teaching this lesson, I like to get students attention for guided practice by bringing in a magic container of my own and already having some items stowed inside to pretend its magic as I show them other possible inputs and outputs for the table.  In this lesson students do work on blank paper and draw their own pots and t-charts.  However, I like to have prepared sheets for students to use especially when I have limited class time.  Math wire happens to have a sheet that fits perfectly with this lesson–just follow the link.http://www.mathwire.com/algebra/magicpotworkmat.pdf.