Addition and Subtraction
- Children solve addition and subtraction differently from adults and each other. Using concrete materials and screens helps determine the strategies that a child will use.
- A child must be able to ascribe numerosity to a collection. This requires one-to-one correspondence and coordinating A NWS.
- Addition and Subtraction tasks involving screened collections are used to help determine students’ ability to use mental strategies to solve addition and subtractive tasks.
- Additive tasks involving one screened and one unscreened collection allows the teacher to determine the level of mental strategies and whether the child needs to see and use items to solve addition and subtraction tasks.
- Solving tasks involving screened collections provides an immediate phase between working with materials and solving tasks involving written number sentences.
Teaching Points:
- Link number word sequences with the addition subtraction that you are developing. e.g. if you are focusing on adding/subtracting 3, practise counting 3 more/less at NWS practice.
- Always use screens to help develop and understanding of addition/ subtraction. Don’t be tempted to tell the children what to do. Use questioning techniques to develop understanding - strategies will develop when the child has made sense of the problem.
- Make sure that the child understands a problem. Screen when they are confident to engender the development of more sophisticated strategies
- Example of screening:
Firstly show addition tasks unscreened (they do not need to be presented in this way but it is beneficial that each group is a different colour). This helps develop the idea that two different groups come together to make one group. The children could put the two groups together and see the two groups within one group.
Ask questions like: What do you see? How man red do you see? How many green do you see? How many are there altogether? How do you know that? Would you like check? (allow self-correction) Why did you change you answer? Why is it ___ and not ___?
This second activity encourages the development of a count-on strategy. It is a good stepping stone because it encourages the child to see the first group as a quantity rather than individual items (Say ” There are four under here.”). The second group unscreened supports the child because he doesn’t have to double count (he can use the counters to keep track of how many counted on.)
Say things like like: There are 4 red counters hiding under here. How many green do you see? How many are there altogether? How do you know that? Would you like check? (allow self-correction) Why did you change you answer? Why is it ___ and not ___?
This intermediate stage enables the child to see part of the problem but encouages the child to use a double count strategy. Some children will use this task in the same way as they use above.
This is the next stage. The child cannot see the counters but they can understand what is being asked because they can imagine what is under the screen. If the child needs reassurance a sneaky peek always helps!
Say things like:There are 4 red counters hiding under here. There are 3 green counters under here. How many are there altogether? How do you know that? Would you like check? (allow self-correction) Why did you change you answer? Why is it ___ and not ___?
- This is only simple addition. It can also be use for subtraction, missing addends and missing subtrahends.
Of course you can use a variety resources. Screens could be: cards, screens, boxes, buckets, hands, etc. Items could be buttons, balls, flat marbles, pine cones, stones, etc.
The Children of Humbie Primary Recommend:
We like using the interactive whiteboards. Layer the picture to start screening.
This was fun. Mrs Stratton says, “There are four people in the farmyard.” (I can see these) “There are some hiding in the house and there are eight people altogether. How many are hiding in the house?…. How do you know?..Would you like to check?”
Money always grabs our attention. Mrs Stratton says, “There was 15p. I took away 9p and put it in the blue purse. How much is left in the pink purse?…How do you know?…Would you like to check? …Prove it another way”
When we start using non-count-by-one strategies we use empty number lines to help us. Here we are practising counting in hundreds, tens and ones on giant empty number lines in the playground. We can annotate these too.
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