I made a set of cards asking questions about a number. Each set of cards was printed on a different color of tagboard. I usually made one set for a group. Because each set was a different color it was easy to keep the sets of questions together. If a card ended up on the floor, I knew who to give it to based on the color. I kept the number of questions to less than twenty. Each group was given a number to use with the questions. Sometimes they took turns flipping a question over and all would write the answer on their boards. Sometimes one would answer the question with the others checking, then another child would answer the next question with all checking, and so on.
I also printed the cards on blue paper. (There's nothing special about blue, one year I printed them on green.) I printed enough so that each child in the classroom had a set. I gave a set of 'blue cards' to parents at conference time and explained how to use them. I explained how the 'blue cards' were now a part of homework in the evening.
I put a picture of some of the cards below. To use them, choose a number. I expected second graders to use a number between 1 and 50 to start with and we worked our way to larger numbers. Actually, I started the same in fourth grade, but I worked them to larger numbers faster than the second graders. The cards are using the number 6 as an example.
The purpose behind the cards was to get the students thinking about numbers in more than one way and to become comfortable with them. Questions could be removed from the stack and new ones added as the year progressed.
My highest level students were allowed to use much bigger numbers and some of the cards were not used with them.