It is always good to know what is expected of children as they work their way through the primary curriculum and we have just published a brief summary of some of the most important addition and subtraction concepts to be taught in Year 4. 1. Mental addition Children will meet a variety of vocabulary associated with addition. These include: more,   add,   sum,   total,   altogether,   increase,   equals,   sign,   inverse. These words should be used as often as possible when talking to children. They need to know that 76 +  54 is the same as 54 + 76 (this is called the commutative law, but children do not need to know the word!) and that: 23 + 13 + 21 can be worked out in several different orders eg 13 + 21 + 23 will give the same answer as the above order. It is important that children have real confidence with adding any two one digit numbers (e.g. 4 and 5 ) and that they know these in a similar way to knowing their tables. Constant recall of these simple facts will make larger mental addition much easier. Strategies for carrying out mental addition need to be discussed frequently - for example, we often start with the tens or hundreds when calculating mentally - the opposite of what is expected when writing a calculation down. Children are also expected to understand that subtraction is the opposite of addition and that it can be used to check addition questions. Where calculators are used the child should make an estimate of the answer first. 2. Mental subtraction Children should be able to read, write and understand the following words: take away,  subtract,  how many are left?,  how much less?,  difference between,  how much more?,  how many more to make?,  decrease, inverse....  and the minus sign (–) They should know that: Subtraction is the same as taking away, finding the difference between and complementary addition. Subtraction is non-commutative. When a larger number is subtracted from a smaller number, the answer is negative. Subtracting a number from another makes it smaller. Subtracting zero makes no difference to a number. Subtraction is the inverse of addition. They should have good mental strategies for solving subtraction problems with simple numbers. If children are going to be confident with mental addition and subtraction they need to be shown how to carry out certain calculations in the easiest way possible. For example: adding 9,  19,  29 etc by adding 10, 20, 30 etc and then subtracting 1. To subtract 9,   19,   29 etc, in the same way, subtract 10,  20,  30 and then add 1. The same process can be carried out with addition and subtraction of 28,   38,    48 etc. It is important to discuss how answers are achieved 'in your head' and explain these methods as they are often very different from doing the same calculation on paper. 2. Written addition and subtraction In year 4 children are expected to build on their mental methods of addition and subtraction to use pencil and paper methods. For more on written addition and subtraction why not have a look at the full report?