This Fluency Activity is a part of the Lesson 12, Unit 6, Grade 2. During Topic C and for the remainder of the year, each day's fluency activities include an opportunity for review and mastery of the sums and differences with totals through 20 by means of the Core Fluency Practice Sets or Sprints. Five options are provided in this lesson for the Core Fluency Practice Set, with Set A being the most simple and Set E being the most complex. Start all students on Set A. Students complete as many problems as they can in 120 seconds. One hundred percent accuracy and completion is recommended before moving to the next level.