I found out about cup stackers 2 years ago when I was in Kindergarten. We use them in P.E. class. They are cups that come in a set of 12 that you stack. The kinds of stacks that you do are:
The Three Stack, The Six Stack, The Ten Stack & The Twelve Stack.
I have two set of cup stackers. One is a mini blue set (which I can't find) and the other is a full sized red set. I really want to buy a mat a timer to go with them but it is $29.99!