Lesson: Reflections on a Coordinate Plane

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Lesson Objective

Students will be able to draw a reflected figure and define the line of symmetry.

Lesson Plan





Start [slide 1] by having students guess how many lines of symmetry each shape has. Write down their guesses.  Go to the Shape Game (http://www.innovationslearning.co.uk/subjects/maths/activities/year3/symmetry/shape_game.asp) linked in the lesson plan. Enter in the guesses. The game will show the correct amount of each lines and a visual of each fold. You could skip this slide altogether and just start with the game itself.


Direct Instruction


[Slide 2] names the objective. [Slide 3] Ask students which axis is the x-axis. They should know and if they don’t, at least notice that it is bright blue. Ask them how we should reflect it over that line. Don’t tell students if they are right or wrong yet, but keep asking for a variety of answers. Then ask them what method makes the most sense. Click through the animation and explain that we are counting squares until we meet the x-axis and then counting down the same amount of squares again to create a new dot.

Ask the students what the new coordinates would be. Ask if they notice anything about the ordered pair. Hopefully students will notice that the new ordered pair is the same except that the y-value is now negative. Ask students why they think that this happened. Guide students into realizing that the x-value stays the same because our dot moved down and not left/right.


Independent Practice


Have students complete [slide 4] and [slide 5] on their own. Circulate the room to check and correct and have student volunteers complete the examples on the board. Point out the patterns of the ordered pairs again, emphasizing that this time the x-value changed and the y-value stayed the same.


Guided Practice


Bring the class back together for [slide 6]. Ask them what we should do with the triangle. Someone will probably volunteer that we should do the same thing we’ve been doing for each vertex of the triangle. Have 3 different students complete each reflection. Now that we have three new vertices, ask the students what we should do. They will volunteer that we connect the dots. Have students call out the new ordered pairs for A, B, and C. Click through the animation to show the correct steps.


Independent Practice


Have students complete [slide 7] and [slide 8] on their own. Circulate the room to check and correct and have student volunteers complete the examples on the board. Wait until a student has drawn the image on [slide 8] and then click to see if the answers line up. [Slide 7] has no animation.


Guided Practice


[Slide 9] Click through until only the title and picture shows up. Tell the students we are going to practice our mini-golfing skills. Explain that T stands for Tee and H stands for Hole and the green figure is the grass. Ask students how we are going to hit the ball into the hole. Many will tell you in a straight line from T to H. Draw the line and show them how it goes outside of the grass and explain that we have to keep it inside the grass. Ask them which wall they would try to bounce their ball off of so that it would go in. Most of them will tell you the far left wall. Click through on the slide so that the directions fade in on the left. Students should be able to reflect H over the far left wall on their own, as well as connecting H’ to T. Again, we want them to realize that we can’t hit the ball outside of the grass. Ask them if they can hit the ball through the wall. When they say no, ask what would happen. They should realize that the ball will bounce toward the hole now. So we erase the line outside of the grass to H’ and connect where the ball hits the wall to the H. We have now constructed the path from tee to hole in one bounce.




In closing, have the students complete the exit slip [slide 10] on the bottom of their worksheet. Leave the instructions from [slide 9] on the board as a guide. Our main goal is to see if they know how to reflect over a line, not necessarily if they can get the ball into the hole.




What Worked


This lesson was pretty straightforward and simple for the kids to understand. I liked that the lesson asked them to reflect and give the new coordinates. The kids could pretty much do all of this on their own until the mini golf slide.


What Didn’t Work


When I originally taught this, I didn’t show them the pattern with the coordinates. Although we wrote the new ordered pair, we didn’t talk about the relationship between the two. That was something I forgot to point until almost the end of the unit and it could have been helpful to discuss this now in order to make connections during the lesson on rotations. Also, the mini-golf exit slip was harder than the example we did during class. It might make more sense to do the harder one first and then leave the picture from [slide 11] for them to do on their own.

Lesson Resources

Reflections on a Coordinate Plane   Classwork
Shape Game
Reflections   Notes


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