I had prepared different jars for testing purposes. Some jars had cold cream, some had cream that had been left out for 12 hours at room temperature. Some had a marble, some didn't. Some had whole cream, and some had half-and-half.
We did a quick hands-up to tell our hypotheses - which would make butter faster? Most children thought cold over warm, marble over non-marble, half-and-half over cream.
We partnered up, and - this was tricky - trying to shake the cream at the same speed as our partner - we tested our theories.
I was surprised at the temperature variable results, but it is explained here (we watched this in class after the experiment):
After that, all that was left was to taste our results. The conclusion: Delicious!