The first time I made these anemometers was when I was teaching sixth grade and the instructions said to tape the cups to the straw. That was a disaster and I was running around like a mad woman with the only stapler I had trying to quickly staple 96 cups to straws. Oh the memories :)
I wised up when I moved to fourth grade. What I do now is pre-staple everything. If I was a rich teacher with unlimited resources and time I would purchase 24 staplers and let the kids make these from scratch but the reality is I don't. NOTE - Try to find straws that aren't flexible. You can use the flexible straws but the cup tends to drag those down. Look for supplies at The Dollar Store, Dollar General, or Big Lots to save money.
I usually pre-staple at home, while watching tv, with a large trash bag next to me, as I finish a set I put it in the bag. Last year I had to make well over 80 (I got very good at it). NOTE - Make about 15-20 more then you actually need. Sometimes the staples come out or the child does something to destroy it and it is easier to hand a child an extra then it is to try to fix or lecture the student.
I give each student a set and then I model how to make one up front in case they want to try it at home (you could have children come up and try the stapling part). The students are then responsible for putting the pin in, getting it into the eraser, and decorating a cup with their name. While this sounds fairly simple it always takes a surprisingly long amount of time (which is fine....just an interesting observation). I then take them outside to test them (great photo op by the way). As irony would have it the day we test them the wind is never blowing. I make them hold them up in the air anyway and time for one minute and we generally all conclude that the wind is blowing at 0 miles per hour. Then the fun begins...
We have several outside vents around our school and I then let students see how fast they can get their anemometer to spin at these vents. This makes everyone happy.
Students get to take them home with them. One year one of our second grade teachers saw us out there and asked one of my classes to come in and teach her students how to make them (they study weather as well). That was a fun lesson as we buddied up a fourth grade student with a second grade student to do this. I was seriously impressed at how kind my fourth graders were with those second graders.