Prepare the foam ahead of class:
Make a small hole with scissors in the end of a piece of foam and push the tube/pen cap into it. A skewer inserted into the tube allows the foam to spin freely on the skewer.
Make small holes in an egg carton cups and push a skewer through them. Hot glue the skewer in place. (Note: the skewers are a little long in the photo - push them further through before glueing.)
Students assemble their anemometer by pushing the cup skewers into the foam in a circle. Three or four cups work, but younger students may have an easier time spacing out four (one on each side of the foam piece). Ideally the cups are all facing the same direction - help younger students to assemble, and allow older students to experiment with cup placement.
Insert a skewer (with no cup attached) into the hole that the pen cap/tube makes in the foam.
Blow into the cups to turn.
Try experimenting with different numbers of cups, and different strength of breath.
A weather station anemometer has metal cups which are weather-proof. The speed of the spinning cups is recorded as wind speed.