This Fluency Activity is a part of the Lesson 28, Unit 4, Grade K. Students find the hidden partners of 10 in support of today's work with composition and decomposition. Conduct the activity as outlined in Lesson 26, but now, have students find partners of 10. Provide each partner with a stick of 10 cubes to help the pair determine the missing part. For example, a student turns over 4 and then breaks off 4 cubes, revealing 6 as the missing part. Students then know to look for the card with the number 6.