We have been working on estimation. Since it is winter, I made an igloo out of blue paper and taped it to the board. I put one square "ice block" on the igloo and asked the kids to estimate how many ice blocks it would take to fill up the whole igloo.
The kids made some estimations and then they helped me fill the igloo with ice blocks. It took 24 whole ice blocks and 6 half ice blocks to fill up the igloo (27 ice blocks altogether). The closest estimate was 21 ice blocks. Try this activity using small ice blocks, medium ice blocks, and then large ice blocks and discuss why the kids' estimates change for each size.