You will learn
- Say that a segment has two endpoints.
- Measure a segment.
- Name a segment.
- Tell segments from lines.
Version 0.2 · expanded edition · built from cited public sources Content is based on the official frameworks and sources listed under Sources and standards. No official endorsement is claimed. Written in the style of common primary school assessments. No exam result is promised.
Student lesson
- A segment is part of a line.
- It has two endpoints.
- We can measure it.
- AB and BA name the same segment.
Words to know
Part of a line with two endpoints.
The end of a segment.
How long.
Tool for measuring.
1. Discover: a pencil
A pencil is a straight piece with two ends. Can you measure how long it is?
2. Understand: line segments
A line segment is part of a line between two endpoints. We can measure it.
- Segment AB is 5 cm long.
- Name it AB or BA.
- Edges of a rectangle are segments.
Idea 1: Segment
A line segment has 2 endpoints. Segment AB has the endpoints A and B.
Idea 2: Measure
If A is at 0 and B is at 7 cm on a ruler, then AB = 7 − 0 = 7 cm.
Idea 3: Naming
AB is the same as BA. A triangle has 3 segments.
Why can we measure it? It has a start and an end.
3. Worked examples
Example 1 (I show you): Endpoints
Segment AB
- Count the ends.
Answer: 2
Example 2 (We do it together): Measure
A at 0, B at 7 cm
- 7 − 0.
Answer: 7 cm
Example 3 (You try): Count
Segments in a triangle
Show the steps and answer
- The three sides.
Answer: 3
Did you know?
The sides of every shape are segments.
Why this matters
Segments are the sides of shapes, the paths we measure.
4. Explore: measure
You need a ruler.
- Draw segment AB 5 cm long.
- Mark the endpoints.
- Measure with the ruler.
- Draw one 8 cm long.
Think about it: what did you notice?
5 cm and 8 cm.
5. Practise
Say it in a sentence
Use these starters when you talk about the lesson. Say them out loud.
- The endpoints are ___ and ___.
- The length is ___ − ___ = ___.
- AB is the same as ___.
- The shape has ___ segments.
Guided practice
Question 1. How many endpoints?
2.
Question 2. Can we measure a segment?
Yes.
Question 3. Edges of a rectangle are?
Segments.
Independent practice
Level 1: Start
- Endpoints of a segment
- Can we measure a line?
- Length of AB if A at 0 and B at 7 cm
- Name another way to write AB
- How many segments in a triangle?
Level 2: Grow
- A at 2 cm and B at 9 cm. Find AB.
- How many segments has a square?
- Name the segment with endpoints X and Y
Level 3: Stretch
- How many segments has a hexagon?
- P at 3.5 cm and Q at 12 cm. Find PQ.
- Ben says AB is longer than BA. What is wrong?
Answers are in the answer key below. Try first, then check.
6. Apply: everyday mathematics
A fence is 12 m between two posts. Is it a line or a segment?
Show a sample answer
A segment.
Another one. A string is stretched between pegs at 5 cm and 17 cm on a ruler. How long is it?
Show a sample answer
17 − 5 = 12 cm
7. Common mistakes
Fix: Use dots for endpoints.
Fix: Subtract the start from the end.
Fix: A segment has two endpoints.
8. Lesson summary and revision card
- I can say a segment has two endpoints.
- I can measure a segment.
- I can name a segment.
- I can tell segments from lines.
9. Check and master
Answer all 14 questions. You will see feedback after each one.
Your result appears here after you answer every question.
10. Key takeaways
- Two endpoints.
- Can be measured.
- Edges of shapes.
11. Next lesson
Next lesson: Rays. Keep going with the next idea in this course.
Exam practice
These questions are written in the style of common school and international primary assessments. Try them on your own, without looking back. Then check your answers in the marking guide. The marks are shown in brackets.
- How many endpoints does a segment have? [1 mark]
- A is at 0 and B is at 7 cm. Find AB. [2 marks]
- Write another name for AB. [1 mark]
- How many segments are in a triangle? Explain. [2 marks]
- Kofi says a segment never ends. Is he right? Explain. [3 marks]
Total: 9 marks.
Marking guide and model answers
- 2 [1]
- 7 − 0 [1]; 7 cm [1]
- BA [1]
- The sides [1]; 3 [1]
- No [1]. A segment has two endpoints [1]. A line is the one that goes on forever [1].
Score guide: 8 to 9 = secure. 6 to 7 = nearly there, revise the parts you missed. Under 6 = work through the lesson again with a grown-up.
Printable worksheet
- Endpoints of a segment
- Can we measure a line? (yes/no)
- AB if A at 0, B at 7 cm
- AB is the same as
- Segments in a triangle
- A line segment has
- A segment can be
- A triangle has how many segments?
- AB is the same as
- A fence between two posts is a
Homework
Measure five segments in your room.
Answer key and marking scheme
| Question | Expected response | Marks |
|---|---|---|
| Endpoints of a segment | 2 | 2 |
| Can we measure a line? (yes/no) | no | 2 |
| AB if A at 0, B at 7 cm | 7 cm | 2 |
| AB is the same as | BA | 2 |
| Segments in a triangle | 3 | 2 |
| Total | 10 |
Practice answers: Worksheet: 1 2; 2 no; 3 7 cm; 4 BA; 5 3.
Quiz answers: 1 A, 2 B, 3 C, 4 A, 5 B, 6 A, 7 B, 8 C, 9 A, 10 B, 11 C, 12 A, Challenge 1 C, Challenge 2 C.
Extra worksheet answers (items 6 onward): 6 2 endpoints; 7 measured; 8 3; 9 BA; 10 segment.
Independent practice answers. Level 1: 1 2; 2 no, a line goes on forever; 3 7 cm; 4 BA; 5 3. Level 2: 1 7 cm; 2 4; 3 segment XY. Level 3: 1 6; 2 8.5 cm; 3 AB and BA are the same segment, so they have the same length..
Mastery and remediation
| Objective | Bronze (Developing) | Silver (Proficient) | Gold (Advanced) |
|---|---|---|---|
| O1 Say that a segment has two endpoints | Shows this with help from an adult or a picture | Does this independently and explains how they know | Explains it clearly and uses it in a new situation |
| O2 Measure a segment | Shows this with help from an adult or a picture | Does this independently and explains how they know | Explains it clearly and uses it in a new situation |
| O3 Name a segment | Shows this with help from an adult or a picture | Does this independently and explains how they know | Explains it clearly and uses it in a new situation |
| O4 Tell segments from lines | Shows this with help from an adult or a picture | Does this independently and explains how they know | Explains it clearly and uses it in a new situation |
Courseversity badge thresholds (overall quiz score): Gold = 90–100%; Silver = 80–89.9%; Bronze = 70–79.9%. A badge is never a full record of progress.
If a learner struggles
- Find the misconception: Using arrows on a segment. Use dots for endpoints.
- Explain another way: use real objects first, then pictures.
- Show a simpler example: Measure objects with a ruler.
- Guided practice: work through one example together and let the learner try the next one.
- Reassess: use the quiz again or the worksheet.
- Move on when the learner shows Silver-level evidence independently.
For parents and guardians
In this lesson your child learns that a segment has two endpoints and can be measured. You do not need to be good at mathematics to help.
- Measure objects at home with a ruler.
- Ask: where are the endpoints?
- Compare a string with a ruler.
- Ask “how do you know?” after each answer, and listen.
- Praise effort, not only right answers. Mistakes are how we learn.
- Ten to fifteen minutes a day is better than one long session.
Teacher package
1–5. Objectives, prerequisites, materials, preparation, duration
Lesson objectives. Learners will: say that a segment has two endpoints; measure a segment; name a segment; tell segments from lines.
Prerequisite knowledge. Lessons 1 and 2.
Materials. Counters (stones, seeds or bottle tops), paper, pencils, board or chalkboard. Low-resource options: use stones, seeds, sticks, bottle tops or drawings in the sand or on the board instead of printed materials.
Preparation. Gather the counters and draw the example pictures on the board before the lesson.
Suggested duration. 45–60 minutes. It can be split into two shorter sessions.
6–9. Teaching procedure, explanation notes, guided and independent activities
Introduction (5 min). Start with the Discover situation and let learners suggest ideas before you teach.
Explanation (10 min). Teach the Understand section with real objects first, then pictures, then symbols and words.
Guided activity (10 min). You need a ruler. Learners follow the Explore steps in pairs.
Independent activity (10 min). Learners complete the independent practice and the worksheet.
Assessment and reflection (5 min). Ask each learner to say one thing they learned and how they know it.
Key questions. Where does it start and end? How long is it?
Teacher explanation notes. Use the concrete, pictorial, abstract order: real objects first, then pictures, then symbols and words. Return to real objects whenever a learner needs support.
10–12. Differentiation, formative assessment, common misconceptions
Support. Use real objects and work with a partner; say each step aloud together. Extension. Ask learners to make up their own example and explain it to a partner.
Formative assessment. Listen to learner explanations, ask “how do you know?”, and check the independent work.
Misconceptions. Using arrows on a segment. Use dots for endpoints.
13–15. Assessment questions, answer keys, marking scheme
Use the quiz and worksheet on this page. The 9-mark exam practice scheme, the 10-mark scheme and all answers are in the answer sections above. Re-check every answer and the marking scheme before publication.
16–19. Remediation, enrichment, homework, teacher reflection
Remediation. Measure objects with a ruler. Enrichment. Invite learners to find or create three more examples at home or in the classroom and explain them. Homework. See above.
Teacher reflection. After teaching, record: which concepts learners understood; which misconceptions occurred; which activities worked; which learners need more practice; and what to improve next time.
Sources and standards
This lesson is based on the sources below, and no official endorsement is claimed. Reference starting points named in the Courseversity standard: Common Core State Standards for Mathematics, Cambridge Primary and the IB Primary Years Programme. Where a standard code is named, it points to the official framework.
Official standards for this topic area. Common Core State Standards for Mathematics (official site): Grade 4 » Geometry. These pages list the standards that cover this topic area; read them alongside the lesson.
Research used to shape this lesson. Common Core 4.G.A.1 and 2.MD.A.1; Cambridge Primary Mathematics Stage 4 (line segments). These sources informed the lesson.