Phase: 
During/Explore/Explain 
Activity: 
 Organize students in groups of 34 students.
 Distribute bags with chips, cubes, and number card deck to each group.
 Students place the deck of number cards facedown where the cards are accessible to the entire group.
 Each student will get twenty snap cubes.
 Student 1 selects a number card from the number card deck and shows that number to the group.
 All students will write that number in their math journal or on a piece of paper and build a train with that number of snap cubes.
 When everyone has built a train, everyone will hold the train behind their back or under the table (where others can not see it) and snap (break) their train into two parts.
 Students will keep one part hidden but place the other part of their trains on the table until it is their turn to share.
 Student 1 shows one part of their train where the group can see it while keeping the other part of the train hidden.
 Students in the group count how many they see and try to be the first to name the number of cubes that are still hidden. The first player to answer correctly must also tell what the equation is with the unknown part. For example, the number card is 12. Student 1 broke the trains so that 4 cubes are showing. Student 2 is the first to give the correct response of 8, but they must also state an equation to match the response, 8! "I see 4 and I know that 12= 4+8." or "I see 4 and 124=8."
 The first player to name the hidden number of cubes and make a correct equation gets one chip.
 Play continues until all group members have shared their trains for 12.
 Students record each equation that is made for 12 in their math journal.
 Round 2 begins with Student 2 selecting a new number card from the deck, repeating the steps above. Play continues, if time permits with each student selecting a number card.
 The player with the most chips after several rounds wins the game.

Assessment Strategies: 
The teacher would use anecdotal notes to assess the students' strategies and understanding using the following questions during the game:  How did you decide how many cubes were hiding?
 How did you decide how to write the equation?
 How is your equation the same as your neighbor's equation? How do they differ?
 How might you organize your equations for this number to show a pattern?
 What else can you know, if you know 12= 8 + 4? What other equations could you write?
 What does the equal sign mean in your equation?
The teacher will collect and check math journals or papers. 

Advanced Preparation: 
 Review Standards for Mathematical Practices that you will focus on during the lesson.
 Review the significant ideas in the standards to connect this lesson with key mathematical ideas for developing an understanding relationship between addition and subtraction.
 Create a list of students who will be grouped into teams of 34 students.
 Reproduce copies of number cards resource, 1 deck for every 34 students. Laminating is suggested to be able to use again for this game and other games.
 Gather enough snap cubes for each group of 34 to have 20 snap cubes.
 Gather 1012 chips for each group.
 Place snap cubes, chips, and the deck of cards for each group of students in small selfclosing bags.
 Provide a math journal or paper for recording equations.

Variation Tips (optional): 
Students can continue to play this game during workshop/center time to demonstrate fluency. After students are comfortable with this version of the game, the game can be varied with students breaking trains into 3 parts. If students are struggling to determine the unknown, give students smaller numbers as well as work with the teacher in a smaller group. 
Notes or Recommendations (optional): 
ALCOS 2019 Mathematics Standards: 6. Add and subtract within 20. a. Demonstrate fluency with addition and subtraction facts with sums or differences to 10 by counting on. b. Demonstrate fluency with addition and subtraction facts with sums or differences to 10 by making ten. c. Demonstrate fluency with addition and subtraction facts with sums or differences to 10 by decomposing a number leading to a ten. Example: 13  4 = 13  3  1 = 10  1 = 9 d. Demonstrate fluency with addition and subtraction facts with sums or differences to 10 by using the relationship between addition and subtraction. Example: Knowing that 8 + 4 = 12, one knows 12  8 = 4. e. Demonstrate fluency with addition and subtraction facts with sums or differences to 10 by creating equivalent but easier or known sums. Example: adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13 8. Solve for the unknown whole number in various positions in an addition or subtraction equation, relating three whole numbers that would make it true. Example: determining the unknown number that makes the equation true in each of the equations 8 + ? = 11, 5 = ? – 3, and 6 + 6 = ?
