While collecting data, the students wrap string around the fullest part of the balloon, and measure the length of the string to find the circumference.
I have the string pre-cut in one meter lengths so that the students don't spend time on that task. In order to keep the string from getting tangled, I fold the length in half three times, the loosely knot the string. Its easy to store these string bundles in a ziploc bag. They don't get tangled, and I don't have to waste materials or spend more time cutting lengths of string.
We use meter length string in our lab for many different tasks, and the students are used to putting the supplies away in the same condition they were given. They have become master string bundlers, and we're never all tied up in knots!
Have you got a hot LAB SUPPLY tip? Let's hear it!