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Angle Detectives

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cheryl.ilaw

Tier 1
For Schools

Lesson Plan

Session 1 Lesson Plan

Students will learn the definition of an angle, practice measuring angles with protractors, and accurately classify them as acute, right, obtuse, straight, or reflex.

Understanding angle definitions and classification is foundational for all geometry topics, improves spatial reasoning, and supports real-world problem solving. This lesson’s hands-on approach and IEP supports ensure all learners can access the content.

Audience

10th Grade

Time

1 hour

Approach

Hands-on exploration and classification

Materials

Angle Definitions Worksheet, Angle Classification Cards, Angle Visual Aid Poster, Protractors and Rulers, and Whiteboard and Markers

Prep

Prepare Materials

15 minutes

  • Print enough copies of Angle Definitions Worksheet for each student.
  • Print and cut apart Angle Classification Cards into sets for small groups.
  • Display Angle Visual Aid Poster at the front of the room.
  • Gather and arrange protractors, rulers, and whiteboard markers.
  • Review angle definitions, measuring steps, and classification criteria to be ready to model each clearly.

Step 1

Engage

10 minutes

  • Show real-life angle examples (corners of textbooks, clock hands, doors) projected or physical.
  • Ask students in mixed-ability pairs to name any angle type they recognize informally.
  • Use peer support: have IEP and non-IEP students collaborate, encouraging verbal explanation of observations.

Step 2

Direct Instruction

15 minutes

  • Introduce formal definition of an angle, referencing the Angle Visual Aid Poster.
  • Demonstrate step-by-step how to align and read a protractor on the whiteboard, thinking aloud each action.
  • Model classifying several angles as acute, right, obtuse, straight, or reflex, using clear visual cues.
  • Conduct quick comprehension check: thumbs-up/thumbs-down for understanding each step.

Step 3

Guided Practice

15 minutes

  • Distribute Angle Definitions Worksheet.
  • Complete the first three problems together: measure the angle, record the measure, and classify it.
  • Use think-aloud strategies and prompt students with sentence starters (e.g., “I measure this angle by…”).
  • Provide visual highlights and extra time for IEP learners, pairing them with supportive peers.

Step 4

Independent Practice

15 minutes

  • Students finish the remaining worksheet problems on their own.
  • Teacher circulates to offer scaffolding: simplified instructions, guided questions, or extended time as per IEPs.
  • Encourage students to use Angle Classification Cards as reference if needed.
  • Monitor understanding and provide on-the-spot corrective feedback.

Step 5

Closure

5 minutes

  • Recap key takeaways: definition of an angle, measurement steps, and classification categories.
  • Exit ticket: each student writes one angle type and its measure range on a small slip of paper.
  • Collect exit tickets to inform next session’s pacing and review needs.
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Worksheet

Session 1: Angle Definitions Worksheet

Objective: Measure angles accurately and classify them as acute, right, obtuse, straight, or reflex.

IEP Supports: Step-by-step prompts, sentence starters, and visual reminders. Refer to Angle Classification Cards as needed.

Part A: Measuring and Classifying Angles (Use Your Protractor)

Follow these steps for each angle below:

  1. Place the midpoint of your protractor on the vertex of the angle.

  2. Align one ray with the zero line on the protractor.

  3. Read and record the measure where the other ray crosses the protractor scale.

  4. Classify the angle.

  5. Measure and classify Angle A:

    [Drawn Angle A Here]

    • Measurement: _______°



    • Classification: ___________________


  6. Measure and classify Angle B:

    [Drawn Angle B Here]

    • Measurement: _______°



    • Classification: ___________________


  7. Measure and classify Angle C:

    [Drawn Angle C Here]

    • Measurement: _______°



    • Classification: ___________________


Part B: Quick Classification Practice

Write the correct angle type next to each measure.

  1. 30°: ___________________

  2. 90°: ___________________

  3. 150°: ___________________

  4. 180°: ___________________

  5. 270°: ___________________

Part C: Angle Vocabulary and Labeling

  1. Complete the sentence using the word bank {rays, vertex}:
    “An angle is formed by two _________ with a common _________.”



  2. In the diagram below, label the vertex and each ray.

    [Angle Diagram for Labeling Here]

    • Vertex: ___________________


    • Ray 1: ___________________


    • Ray 2: ___________________


Part D: Real-World Angle Detective

Draw or describe an example of an obtuse angle you see in your environment (e.g., door hinges, rooflines). Then:

• Sketch or describe it below:











• Label its vertex and rays, and state its approximate measurement:





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Activity

Session 1: Angle Classification Game

Objective:
Reinforce students’ ability to identify and classify angles (acute, right, obtuse, straight, reflex) in a collaborative, hands-on game.

Materials:

  • Angle Classification Cards (one deck per group)
  • Sorting mats labeled with each angle category (acute, right, obtuse, straight, reflex)
  • Protractors (one per student)
  • Timer or stopwatch
  • Score sheets and pencils

Group Setup:

  • Form small groups of 3–4 students, mixing IEP and non-IEP learners for peer support.
  • Each group places their sorting mats in the center of the table and shuffles their deck of classification cards face down.

How to Play

  1. Draw & Measure (5 minutes per round)

    • On “Go,” Player 1 draws the top card and lays it face up.
    • The player measures the angle on the card with a protractor and announces the measurement.
    • The player places the card on the corresponding category mat.

  2. Group Verification

    • Group members use a provided sentence starter:
      “I measure this angle by aligning the ___ of the protractor at the ___, and I read ___°.”
    • Peers confirm or help correct the classification. If the group disagrees, they revisit measurement together.

  3. Scoring

    • Correct classification earns 1 point for the group.
    • If peers catch and correct an error before the next turn, the group still earns the point (promotes collaborative checks).

  4. Rotate Turns

    • Pass the deck clockwise. Continue until all cards are sorted or time expires.

  5. Winning

    • Total group points. Celebrate all groups that classify at least 80% correctly.

IEP Accommodations & Supports

  • Color-Coded Cards: Each angle type has a distinct border color to assist visual learners.
  • Sentence Starters: Printed on each mat (e.g., “This is an obtuse angle because ___.”).
  • Peer Buddy System: Pair students who may need extra support with a “math buddy” to model measurements.
  • Extended Time: Groups may pause the timer for up to 2 minutes per round to discuss challenging angles.
  • Checklists: Provide each student a checklist of classification steps:
    1. Place protractor midpoint at vertex.
    2. Align one ray with zero line.
    3. Read measure.
    4. Match to category.

Closure & Reflection (5 minutes)

  • Gather as a class. Invite each group to share one angle that challenged them and how they resolved it.
  • Exit prompt: “Name one strategy your group used to ensure accurate classification.”

Extension:

  • For early finishers, challenge them to create two new angle cards: one reflex and one acute. Swap decks with another group for bonus classification practice.
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