Add 2-digit numbers when crossing the tens boundary
Lesson details
Learning outcome
I can add two-digit numbers when the sum crosses the tens boundary
Key learning points
- When adding two-digit numbers that cross the tens boundary, both addends can be partitioned, then recombined.
- When adding two-digit numbers that cross the tens boundary, one addend can be partitioned. This is more efficient.
- A number line can be used to find a missing addend when the tens boundary is crossed.
Keywords
Partition - To split a whole up into parts; a piece or section of a whole.
Common misconception
If children partition both addends when addition involves bridging 10, they may forget to add the extra 10 made when combining the ones.
Encourage children to consider whether an addition will bridge 10 before solving and if so, partition only one addend to reduce the number of steps required, increasing efficiency.
Teacher tip
Encourage children to notice and articulate patterns as they work so they can begin to mentally manipulate numbers and work in the most efficient way. Ensure that a focus remains on the use of efficient strategies to avoid children defaulting to counting in ones.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.Which digit is missing in this equation?
Q2.Which of the following is the missing addend?
Q3.Use the first equation to help solve the second equation.
Q4.Which of the following could be the ones digits in the equation?
Q5.One of the Base 10 blocks has been moved over from one addend to the other. Which of the following could show the new equation? Tick two.
Q6.Find the missing addend.
Assessment exit quiz
6 Questions
Q1.Partition both addends to solve the equation. 57 + 34 =
Q2.Which of the following is correct?
Q3.Find the missing whole in the bar model.
Q4.Which equation is represented by this number line?
Q5.Which of the following is the missing addend? 35 + = 71
Q6.Find the missing addend. 38 + = 63
To help you plan your 2 maths lesson on: Add 2-digit numbers when crossing the tens boundary, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 2 maths lesson on: Add 2-digit numbers when crossing the tens boundary, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 1 maths lessons from the Addition and subtraction of two 2-digit numbers unit, dive into the full primary maths curriculum, or learn more about lesson planning.