Click here to see how to play. Basically, a "set" of 3 must have characteristics that are either all the same or all different. The characteristics are as follows: color (red, purple, green), shape (diamond, squiggle, round), number (one, two, or three), and inside (solid, striped, or open). You can have, for example, a set of all green or a set of one green, one red, and one purple. So all must be the same, or all must be different. This must continue for all of the characteristics.
Here is an example from https://mrrgteacher.wordpress.com/category/family-math-night/
The top left is a set because they are all different colors, all different shapes, all different numbers, and all different insides.
The top right is a set because they are all the same colors, all different shapes, all same numbers, and all different insides.
The bottom is NOT a set because although all colors and numbers are the same, the insides have 2 the same (solid) and one not (striped.) The rules are all the same or all different, so you cannot have two the same and one different.
Three years ago, one of my classes finished all 6 sets in 21 seconds...no one has beat them...yet!