12 centers differentiated at three levels of ability for a total of 36 activities. Each center activity has a corresponding common core alignment. Levels were determined by the following criteria: Level 2 is where a first grader should be performing at this point in the school year. Level 1 is a skill that should already be master. It may even be kindergarten review. Level 3 is a skill that should be mastered by the end of first grade, OR it may be a second grade skill.