Line Segments, Rays, & Angles

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SWBAT will learn terms to identify lines and angles.

Big Idea

Lines and angles can be described with special names. A line segment has 2 end points. Angles can be acute, obtuse, right, or straight.


10 minutes

In today's lesson, the students learn to identify and draw line segments, rays, and angles. This aligns with 4.GA.1 because the students will be able to identify these in two-dimensional shapes.  This is an important skill for the students because this leads into identifying shapes by their lines and angles.  

 To get started, we review the skills from the previous day.  "Someone raise your hand and describe a line for me."  I let a few students share their answer.  One student says, "A line has arrows on the end."  I then ask, "Which end?"  This is to ensure that the students understanding exactly what they are talking about.  A student responds that there are two ends.   To use this as another teaching opportunity and to make sure that all students understood the previous lesson because it is important to today's lesson, I continued to question the students.  "Someone explain to me what do those arrows mean on a line?"   A student responds that it means that the line goes on in both directions.  Another student adds,"It never stops."  I let the students know, "Today, we aregoing to talk about line segments, rays, and angles."


Whole Class Discussion

15 minutes

I call the students to the carpet as we prepare for a whole class discussion.  The power point is already up on the Smart board.  I like for my students to be near so that I can have their full attention while I'm at the Smart board.  

I begin by going over important vocabulary for this lesson.  The students will have to know these terms to understand the lesson.


Line Segment - Part of a line with two endpoints.

Ray - Part of a line that has one end point and goes on forever in the other direction.

Angle - A figure formed by two rays that have the same endpoint.

Right angle - a  square corner

Acute angle - less than a right angle

Obtuse angle - greater than a right angle

Straight angle - forms a straight line

 I pose a scenario.  "Teresa and Michael are in the same math class.  Teresa said that a  line segment is different from a line.  Michael disagreed.  Who is correct?"  I let the students think about the question.  "Share your answer with your neighbor."  By doing this it allows students to share their way of thinking, as well as it may help some students who do not know how to come up with the answer.  I take a few student responses.   Some of the student responses:  "Teresa is correct because a line segment has points and a line has arrows on both ends."  I ask the students to explain to me what the points mean on a line segment.  I call on one of my ESL students, who is usually quiet and reserved.  He shares that the points mean that it stops.   

I draw a line and a line segment on the Smartboard.  I explain to the students that a line segment stops in both directions.  A line segment is just a part of a line.  I model this by circling a piece of a line to show that a segment can be taken from a line.  Also, I label the line with letters to show that a line segment could be from one point to another point on a line.

 Next, we discuss the different types of angles.  Using the powerpoint, we discuss each of the angles.  I make it clear to the students that angles are formed from two rays.  Also, I go back to the definitions in the powerpoint.  I bring it to the students attention that each definition refers back to the right angle.  The acute angle is smaller than a right angle.  The obtuse angle is greater than a right angle.  "If you learn a right angle, then you will learn the rest."  To give the students practice, I have the students modeling angles with their arms.  This is a fun way to get the students excited about learning a new skill.  

I let them know that we will learn about measurement tomorrow. 

Group or Partner Activity

20 minutes

I give the students practice on this skill by letting them work together.  I find that collaborative learning is vital to the success of students.  Students learn from each other by justifying their answers and critiquing the reasoning of others.

For this activity, I put the students in pairs.  I give each group a Group Activity Sheet on Line Segments, Rays, and Angles.  The students must work together draw line segments, rays, and angles (MP4).  They must communicate precisely to others within their groups. They must use clear definitions and terminology as they precisely discuss this problem.  Upon completion of drawing models, the students must go on a scavenger hunt around the classroom identifying items that have acute, right, obtuse or straight angles.  The students explain why they labeled the items as they did by using attributes that clearly separate the groups.

The students are guided to the conceptual understanding through questioning by their classmates, as well as by me.  The students communicate with each other and must agree upon the answer to the problem.  Because the students must agree upon the answer, this will take discussion, critiquing, and justifying of answers by both students (MP3).  From the video, you can hear the students discuss the problem and agree upon the answer to the problem.  As the pairs discuss the problem, they must be precise in their communication within their groups using the appropriate math terminology for this skill.  As I walk around, I am listening for the students to use "talk" that will lead to the answer. I am holding the students accountable for their own learning.  

As they work, I monitor and assess their progression of understanding through questioning. 

1. Describe a line segment?

2. What makes an angle?

3. What's the difference between a ray and a line?

As I walked around the classroom, I heard the students communicate with each other about the assignment.  From the video, you can hear the classroom chatter and constant discussion among the students.  Before Common Core, I thought that a quiet class working out of the book was the ideal class.  Now, I am amazed at some of the conversation going on in the classroom between the students.  

Any groups that finish the assignment early, can go to the computer to practice the skill at the following site until we are ready for the whole group sharing.


15 minutes

To close the lesson, I have one or two students share their answers.  This gives those students who still do not understand another opportunity to learn it.  I like to use my document camera to show the students' work during this time.  Some students do not understand what is being said, but understand clearly when the work is put up for them to see.

I feel that by closing each of my lessons by having students share their work is very important to the success of the lesson.  Students need to see good work samples, as well as work that may have incorrect information.  More than one student may have had the same misconception.  During the closing of the lesson, all misconceptions that were spotted during the group activity will be addressed whole class.  


This was a pretty straight forward lesson.  By the end, the students understood how to identify a line segment, ray, and angle.  I feel that we need to continue to work on identifying the rays that make up an angle.  For example, for angle ABC, the students need to be able to identify the two rays as ray BC and ray BA.  We will practice this skill for board work the next day.