Adding Across Tens

Overview

This 25-minute lesson is designed for Year 3 students to develop and secure their understanding of addition where the ones digit crosses ten—e.g., adding 8 + 7. The focus aligns with the National Curriculum for England’s Year 3 programme of study in Mathematics, specifically:

• Number – addition and subtraction:
  Add and subtract numbers mentally, including: a three-digit number and ones

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Learning Objectives

By the end of the lesson, students will:

• Understand how to add single-digit numbers that result in a sum greater than ten.
• Develop mental strategies to add 1s crossing tens (e.g., 8 + 7 = 15).
• Use place value knowledge to partition numbers and add efficiently.
• Demonstrate confidence in adding across the ten boundary using a range of representations.

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Curriculum Links

• Mathematics – Number: addition and subtraction (Year 3)
  Pupils should be taught to:
  • Add and subtract numbers mentally, including: a three-digit number and ones
  • Recognise the place value of each digit in a three-digit number (hundreds, tens, ones)
  • Solve problems, including missing number problems, using number facts, place value, and more complex addition.

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Resources

• Whiteboards and markers
• Place value counters or Diennes blocks (tens and ones)
• Number cards (0-20)
• ‘Addition across tens’ number line mats
• Worksheet with 10 addition questions crossing tens
• Visual models (e.g., bead strings or digit cards)

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Lesson Structure

1. Introduction (5 minutes)

• Engage: Start with 2 quick mental addition questions that do NOT cross ten, then 2 that DO cross ten (e.g., 7 + 3). Ask students if they notice any difference in how they do these sums.
• Explain: Introduce the concept of 'adding across ten' – when 1s add up to more than 10, and how it involves 'carrying over' to the tens place.
• Use a place value chart and demonstrate with counters (e.g., 8 ones + 7 ones = 15 ones → 1 ten and 5 ones).
• Emphasise that understanding place value helps make adding easier and faster.

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2. Guided Practice (10 minutes)

• Display numbers on cards (e.g., 9 + 5, 6 + 7) and work through adding these as a class.
• Use Diennes blocks for visual support, asking students to physically group ones and then exchange ten ones for one ten.
• Students practise writing the equation and the expanded form (e.g., 9 + 5 = 9 + 1 + 4 = 10 + 4 = 14).
• Introduce the number line mats; model how to "jump" from the starting number past ten using hops of 1 and then the rest.
• Pair students to try two of these problems using the number line and Diennes blocks, encouraging verbal explanation of their thought process.

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3. Independent Activity (7 minutes)

• Hand out a worksheet with 10 addition questions where the ones cross ten (e.g., 7 + 6, 8 + 7, 5 + 9).
• Students can use whiteboards, number lines, or counters to solve the problems.
• Circulate and support individual learners, encouraging use of partitioning and place value vocabulary.

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4. Plenary (3 minutes)

• Ask students to share one strategy they found helpful when adding across tens.
• Quick quiz: Call out sums, and students give answers aloud, explaining their reasoning briefly.
• Reinforce how mental addition across tens is a key stepping stone toward adding larger numbers efficiently.

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Assessment

• Formative assessment through observation during guided and independent work.
• Check student explanations and written work for correct place value use and understanding of crossing ten.
• Use plenary responses to gauge confidence and identify any misconceptions.

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Differentiation

• Support: Provide extra hands-on counters and number lines; work closely with small group intervention.
• Challenge: Extend to adding 2-digit numbers across tens (e.g., 27 + 8) or introducing simple column addition methods.

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Extension Idea

• Incorporate an interactive classroom ‘number hop’ game where children physically jump along a giant floor number line to model addition across tens kinaesthetically.

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By integrating visual, verbal, and physical strategies, this lesson actively engages Year 3 learners in mastering the essential skill of adding ones across tens, building solid foundations for future number work in line with the National Curriculum.