Number Talk Activities

Subitizing With Dot Cards
Subitizing means to instantly recognize a quantity without counting, is a foundation skill for students and listed as one of the six components for number sense. In Kindergarten students play with subitizing all year, beginning the first month of school.
I begin with small numbers like three and four using dot cards in a small group of about six students. First I invite them to tell me the number, accepting all answers. I record the answers and then ask them how they figured out the number. Talking about their thinking is a great opportunity for students to learn from each other as they hear the many different ways that the number is figured out (2 + 1, 3+0, 1+1+1).
As they gain experience I increase the complexity of the the dot card as well as the number of dots. Once students have mastered numbers to six, I change my format and use it as a pre-math warm-up and do finger flashes* with quick peaks at the number cards to build fluency. At the same time, I add dot cards to my math work stations so that students are continuously building fluency.
*Finger flashes are when students show the number using fingers instead of voice. It allows students to do their own their own thinking and everyone to provide their own answer to the challenge. The pace is not interrupted by calling out and you can proceed with speed to build fluency. While you can do finger flashes with whole group (and I do), it is much easier to see students response and keep the speed at a fast pace with six students.
I make my own dot cards using a bingo dobber or stickers and file cards. For math work stations I cut file cards in half while for teaching I use oversize file cards and round stickers. Here is an example of a popular game that I include at my math work stations.

Turn over a dot card and add that number of blocks to your mat. Keep going until all of the cards have been used, then build a structure using only those blocks. 
This is usually a partner game with each player having their own work mat. Note that these dot cards are made with a bingo dobber.