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Calculating mentally

As well as developing an increasingly sophisticated concept of ten, students display their thinking about addition and subtraction through three procedures:

  1. a mental replay of the written algorithm
  2. a counting-based approach to building on (or decreasing) from one number in tens and ones (the jump approach)
  3. a collection-based approach, allowing separation and recombining of tens and ones (the split method).

These different approaches mean that the tens and ones level has two elements: one describing the jump method and the other the split method. Both ways enable students to add and subtract two-digit numbers in the absence of any concrete materials.