Calling All Doctors...Help with Balancing Equations

Okay, I'm on a roll with freebies this week!  Today the 2nd grade math para and I were trying to think of a good way for students to balance equations when there were missing addends.  Students were not grasping that they would have to balance the equation by reading from left to right.  You may be able to run to the printer faster than I can.  What tricks do you have for students balancing equations?  Please share!