These two young girls are playing "I Have More" which simply involves both players turning over one domino and calling out the number of dots on the domino when adding both sides together. The person with the largest number on their domino wins that round and takes both.
More advanced or older students can either multiply instead of add, or they can draw two and calculate the sum of both dominoes. As with the previous version, highest total wins. Since these dominoes are not being used in a traditional domino game, having a full set is irrelevant. This set of dominoes was picked up by a parent at a garage sale for $1.
This video is worth watching just to see how gracefully Nadia handles Janice, who is determined to win no matter what!