• Mastery PD Materials

Composition of numbers: 20–100

Spine 1: Number, Addition and Subtraction – Topic 1.9


Build on multiples of ten, by introducing non-zero values in the ones place; apply the partitioning structure to these two-digit numbers, decomposing them into tens and ones.

Teaching points

  • Teaching point 1: There is a set counting sequence for counting to 100 and beyond.
  • Teaching point 2: Objects can be counted efficiently by making groups of ten. The digits in the numbers 20–99 tell us about their value.
  • Teaching point 3: Each number on the 0–100 number line has a unique position.
  • Teaching point 4: The relative size of two two-digit numbers can be determined by first examining the tens digits and then, if necessary, examining the ones digits, with reference to the cardinal or ordinal value of the numbers.
  • Teaching point 5: Each two-digit number can be partitioned into a tens part and a ones part.
  • Teaching point 6: The tens and ones structure of two-digit numbers can be used to support additive calculation.
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