I started by writing the number 12 on a piece of blue construction paper (for the sky)... :)
I gave each table group a plate full of chalk and they had to choose 5 different colors to trace the number 12.
The end result is a "rainbow 12." (This is also a good technique to use with crayons and practice tracing over sight words.)
The next step is to draw 12 snowflakes with chalk around the number.
The last step, is I have each child count out loud their 12 snowflakes. This allows me to quickly assess their counting and to make sure they have the right amount!
Here are some other options for chalk math:
Choose the number and draw a winter scene using the same number of snowflakes.
Dividing the paper into squares to make the correct number of snowflakes.