Flexible grouping or Differentiated Instruction is a strategy to help the teacher determine if every student in his/her classroom has an understanding of the curriculum standard. If they do not, the teacher can pull that student and find out where his/her misconceptions are and provide direct further instruction.
Differentiation is a way of teaching; it’s not a program or package of worksheets. It asks teachers to know their students well so they can provide each one with experiences and tasks that will improve learning. As Carol Ann Tomlinson has said, differentiation means giving students multiple options for taking in information (1999). Differentiating instruction means that you observe and understand the differences and similarities among students and use this information to plan instruction. (Resource: What is Differentiated Instruction?)
This video was filmed at W.B. Simpson Elementary School.