Year 3 Term 2

Key Concepts – Number – Addition and Subtraction

• That addition follows the commutative law (can be done in any order) but subtraction isn’t.
• That the inverse of addition is subtraction and vice versa and that we can use this to help check our answers.
• Understanding that numbers can be broken into pieces that makes it easier to calculate such as relating numbers to 5 and 10 which helps with number bonds to 20 such as 8 + 7 = 8 + 2 + 5 = 15 – This concept helps when working with larger numbers.
• That any number smaller than 100 has a complement to make 100, and that we can use this to help find compliments to 1000.
• That one less than 10 is 9, 1 less than 100 is 99 and that one less than 1000 is 999
• That when adding multiples of ten, the ones digit doesn’t change, and when you add multiples of hundred, the ones and tens digit do not change.
• That when you add one digit numbers together and they total a number greater than 10, you must then partition this number into tens and ones, and add the tens onto the ten column
• Counting on can be helpful when subtracting – this is particularly helpful when subtracting a large number from a large number ie
• Counting is helpful when subtracting - when subtracting a small number from a large number.

Key Vocabulary – Addition and subtraction

Total

Equal to

Sum

Ones, tens, hundreds and thousands

Difference between

Subtract

Take away

Add

Addition

Plus

Make

How many more

How many less

Key Concepts – Perimeter

• That perimeter is used with 2D shapes
• That perimeter can be calculated by adding the length off all of the sides of a shape together.
• That perimeter allows you to calculate the total distance around the edge of a shape
• That children understand the value of mm, cm and m and how to convert between these measurements
• That children can work out the perimeter of a rectangle if they are given the measurement of one length and one width, and that children can work out the perimeter of a square if they are given the measurement of one side

Key Vocabulary – Perimeter

Length

Width

Perimeter

Measure

Scale

Estimate

Centimetre

Millimetre

Metre

Common Misconceptions – Addition and Subtraction

Children often thing that you can’t use counting on to solve subtraction calculations, - counting on is often the most effective method when numbers are close together.

That children do not understand the value of the whole number and rather see it as a series of singular numbers. This will cause problems when it comes to crossing boundaries.

That subtraction is not commutative and you are not able to take a larger number from a smaller number when working with positive numbers

Common Misconception – Perimeter

That children calculate perimeter by multiplying the length and width of a shape rather than adding the sides of the shape.

That children will not check the unit of measure for each side and therefore have errors in calculating their answer.

That children will put the start of the ruler at the beginning of a side to measure it rather than putting 0 at the start of the line.

That children can be confused by scaling – eg using 1cm to represent 1m and 1m to represent 1km (often used in worksheets)