I came across this game in a NCTM magazine last week and decided to try it out with a student. It helps develop number sense and better understand expanded form/place value.
I took one calculator for us to share. I asked him to create a three-digit number and tell me what it is. He created the number 745 (which he said was an odd number). I told him that we wanted to "wipe out" the tens column so that it reads as a zero. I wanted to see what he did first without me prompting him, so he verbalized what he was doing with the calculator so I could do the same on mine. At first, he wanted to just subtract 4, but we saw that if we take 745-4 that equals 741. This did not wipe out the four in the tens column like we wanted to do. I reminded him of expanded form for numbers (700 + 40 + 5 = 745), which helped to guide him through his next steps. He subtracted 40 from 745, leaving us with a total of 705, thus successfully wiping out the tens column!
This game can be used for the whole class, with points awarded for students who "wipe out" a digit to read as a zero or disappear completely. Here's another example:
Student A: (enters the number 4,307) Wipe out four (passing calculator to classmate)
Student B: (Enters - 400 = . The display shows 3,907. Realizing something is wrong, she does not score a point. Then she enters the number 5,713) Wipe out 5 (passes calculator back)
Student A: (Enters - 5,000 =. The display shows 713, so a point is awarded.
The game continues back and forth until time is stopped by the teacher.