Addition Detectives

Teach Starter Publishing
9 x lessons | Suitable for years: 3

This Mathematics unit covers a range of mental computation strategies for addition.

It consists of 8 lessons of approximately 60-minutes duration.

The sequence of lessons and suggested time frames should be regarded as a guide only; teachers should pace lessons in accordance with the individual learning needs of their class.

An assessment task for monitoring student understanding of the unit objectives is included and will require an additional lesson.


  • To reinforce student understanding of basic addition principles, using concrete materials.
  • To recall 'friends of ten' facts and use this knowledge to solve addition sums.
  • To explore the jump strategy for adding two- and three-digit numbers.
  • To explore the use of number boards/hundreds charts when adding numbers.
  • To progress student understanding of mental addition by partitioning numbers into place value to help them find a total.
  • To investigate the relationship between addition and subtraction.
  • To build upon students' understanding of addition and subtraction by exploring compensation.
  • To reinforce that students can choose to use different addition strategies in different situations.
  • To assess students' understanding of working with place value to solve problems, the connection between addition and subtraction, and the development of efficient mental strategies for computation.

Preparing for Learning

Addition Detectives is themed as an investigation in which students will uncover a new suspect at the end of each lesson. The unit concludes with the students narrowing down the list of suspects until only one remains.

Prior to commencing the unit, familiarise yourself with the Addition Detectives – Teaching PresentationThis presentation contains a consolidation activity for each lesson and will reveal the new suspects.

Create a display in the classroom by printing the Suspect Board Wall Display. Place the banner in a central location and put the pictures of the suspects in a large envelope (or similar), ready to add them to the display during each lesson.

This unit covers a range of addition concepts and strategies that increase in complexity. Teachers are encouraged to browse each lesson before beginning the unit and to adapt the lessons and teaching resources to suit the needs of their students.



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