Number 100

Overview

In this lesson, students explore the number 100 as a significant quantity and analyse how it can be made in different ways using concrete materials. Students connect “100” to representations, number facts, and simple addition strategies.

Learning intentions

• Students will explore what makes 100 using counting, grouping, and adding.
• Students will analyse different representations of 100 (ten-frames, base-ten blocks, number lines, and simple equations).
• Students will compare ways of making 100 and explain their thinking using appropriate language (e.g., “I made 100 by…”, “Because…”).

Success criteria

• I can show 100 using base-ten materials and explain how I know it is 100.
• I can make 100 in different ways and record at least two addition combinations.
• I can use a number line or ten-frame to represent how my combinations reach 100.
• I can tell what stays the same or changes when making 100 in a new way.

Curriculum links

• Number and place value: understanding and representing two-digit numbers up to 100, including composing and decomposing numbers.
• Addition and subtraction (early strategies): using part-part-whole and counting-on to solve addition problems and check reasonableness.
• Mathematical reasoning and communication: describing and comparing number strategies using representations.

Lesson structure (30 minutes)

1. 0–4 min: Hook with “Build 100”

• Teacher displays a large “100” card and asks: “What do you notice about this number?” Students share ideas (e.g., “It’s the biggest number we’re using today.”).
• Quick class chant: “100 is one hundred. Let’s build it.”

2. 4–10 min: Hands-on build and count

• In pairs, students use base-ten blocks (or bundles of 10 and single ones) to build 100.
• Teacher circulates: “How did you make sure it is 100?” Students point to rows/columns and count by tens, not ones.

3. 10–15 min: Representations on ten-frames

• Students choose one ten-frame worksheet or mini-whiteboard: show 100 using ten-frames (e.g., 10 groups of 10).
• Teacher models one example: “If I have 10 rows of 10, that is 100.” Students fill/colour rows in a colour key.

4. 15–22 min: Analyse combinations to make 100

• Teacher introduces the target: “We can make 100 by adding two groups. Today we will find different ways.”
• Students work with concrete materials to find at least two addition combinations (for example, 50 + 50, 60 + 40, 70 + 30). They record using simple equations with teacher support.
• Students must check using a representation (base-ten blocks or number line) rather than guessing.

5. 22–27 min: Quick share and compare

• Students do a “Gallery Walk” at the board: 3–4 students hold up their equations/representations.
• Class discussion prompts: “What is the same in these ways?” “What is different?” “How do you know you didn’t make 99 or 101?”

6. 27–30 min: Exit ticket—show one way

• Students complete a short exit ticket: draw one representation of 100 and write one addition combination that equals 100.
• Teacher collects to review common misconceptions (e.g., making 90 or 110, skipping counting-by-tens).

Resources

• Base-ten blocks (ones, tens, hundreds) or bundled tens and a “hundred” envelope
• Ten-frame cards/printouts (capacity for showing many groups or a clear “10 rows of 10” method)
• Coloured counters or pencils for colouring “rows of 10”
• Number lines (0–100) for teacher and small-group use
• Mini-whiteboards and markers (optional)
• Recording sheets for addition combinations (sentence starters included)
• Exit ticket slips
• Visual “100 is one hundred” anchor chart (built from concrete examples)

Assessment

• Formative: teacher observation during building tasks (“How did you know it was 100?”).
• Formative: collected exit tickets showing representation + one correct addition combination.
• Diagnostic focus: whether students use counting-by-tens/structure of place value instead of relying on counting by ones.

Differentiation

• Support for neurodivergent learners: clear step-by-step roles in pairs (builder, checker, recorder); short tasks with visual time cues.
• Support for EALD: sentence starters for explaining strategy (“I made 100 by…”, “First I… then I…”); model vocabulary with gestures (tens, ones, rows, groups).
• Visual supports: provide a pre-made example ten-frame/representation to reduce cognitive load; allow students to label “tens” and “ones” instead of writing lots of words.
• Manipulatives-first: students who struggle with writing can demonstrate combinations with blocks first, then record one equation with teacher assistance.
• Extension for advanced learners: provide an “Add to 100” challenge card set requiring students to find combinations with specified pattern constraints (e.g., “Find two combinations where one number is 80” or “Find combinations that keep the difference the same”). Students must also explain the strategy used (e.g., “I took 20 from one group and gave it to the other.”).

Extension (optional)

• Challenge: “Find 4 different addition combinations that equal 100. Use at least two different strategies: (1) build with blocks, (2) use a number line or tens/ones, (3) use make-10 thinking extended to 100.”