Grade 3 · Low-Tech Builds · Lesson 76

Model Door Latch

Make a cardboard door with a sliding latch that a partner can open and close.

Time2 × 45 minutesTeamsPairs; alternate builder and testerEquipmentBasic classroom materials; no powered equipment

Your project in view

What you are making

Make a cardboard door with a sliding latch that a partner can open and close.

This generated example illustrates one possible finished design—not actual student work. Use the lesson’s sizes, connected parts and safety steps; your colors and creative details can be different.

Generated finished-project example for Model Door Latch: Make a cardboard door with a sliding latch that a partner can open and close.
Model Door Latch · Generated project example

Student directions · Grade 3

What will you make and do?

Make a cardboard door with a sliding latch that a partner can open and close.

Teacher overview: Students will plan the specific object described below, make and test a first version, then use their results to improve it. Read one step together, demonstrate the unfamiliar action, and let students complete that step before moving on.

  1. 1Plan your project

    Draw the door, hinge and sliding latch. Mark where the latch will enter a keeper on the frame.

  2. 2Make the first parts

    Tape one edge of the door to the frame as a flexible hinge. Check free movement.

  3. 3Put it together

    Make two paper loops to guide a card sliding bar. Add a keeper loop on the frame and a large pull tab.

  4. 4Test it fairly

    Open and close the latch five times. Record catching, tearing or accidental opening.

  5. 5Improve one part

    Change one loop gap or bar width. Repeat the same five cycles without forcing it.

  6. 6Show and turn in

    Show the model door and labeled sliding parts with your cycle results.

How will you know it works?

  • Latches and unlatches by hand
  • Door swings freely when unlatched
  • Record the stated test and explain one revision

Before you move on

Tell a partner what you are making. Point to the part you will work on next. Draw or dictate your test notes if writing slows you down.

Machine cutting, printer setup and electrical power-on require adult approval. A basic-materials model is a valid way to demonstrate the design when equipment is unavailable.

Keep your plan, test notes and before-and-after evidence with the printable design brief below. Use the detailed teacher plan and any coding guide for tool instructions. These steps continue across the lesson’s meetings, not all in one sitting.

For teachers

Engineering standards

This shows how the lesson connects to the national NGSS engineering standards and what student work you can collect.

Assessed

3-5-ETS1-1

Define the need in Make a cardboard door with a sliding latch that a partner can open and close. Agree on the two success checks and the listed material limits.

What students show: Two labeled ideas with the target and limits stated.
Practiced

3-5-ETS1-2

Compare the ideas using the project checks: Latches and unlatches by hand; Door swings freely when unlatched.

What students show: A selected design with a reason connected to a success check.
Assessed

3-5-ETS1-3

Test, change one feature and retest: Open and close the latch five times. Record catching, tearing or accidental opening. Change one loop gap or bar width. Repeat the same five cycles without forcing it.

What students show: Before-and-after results collected under the same conditions.

Materials

  • Cardboard frame and door
  • paper strips
  • tape
  • scissors
  • ruler
  • Pencil, planning paper and the printable design brief below

Teacher preparation

  1. Gather per-pair materials: Cardboard frame and door; paper strips; tape; scissors; ruler.
  2. Make one rough sample and rehearse the exact test: Open and close the latch five times. Record catching, tearing or accidental opening.
  3. Set the size, load or distance marks mentioned in the steps before class. Demonstrate an ordinary first attempt, not a perfect model to copy.
  4. Prepare any holes, fasteners or difficult cuts for students. Check the stated safety note and clear the testing space.

Step by step

How to teach it

Meeting 1 · 0–8 min

See the job and plan

  1. Introduce the finished object: Make a cardboard door with a sliding latch that a partner can open and close.
  2. Draw the door, hinge and sliding latch. Mark where the latch will enter a keeper on the frame.
  3. Students say what would count as a successful result.
Meeting 1 · 8–18 min

Model the unfamiliar action

  1. Demonstrate slowly: Tape one edge of the door to the frame as a flexible hinge. Check free movement.
  2. Pause so partners can repeat the action; provide prepared parts if cutting or folding blocks progress.
Meeting 1 · 18–35 min

Build the first version

  1. Make two paper loops to guide a card sliding bar. Add a keeper loop on the frame and a large pull tab.
  2. Partners swap builder and checker roles halfway through. Check the working part before decorating.
Meeting 1 · 35–45 min

Try once and save

  1. Run one trial of the stated test to locate an obvious problem. Do not count a changed procedure as a fair comparison.
  2. Label and store the model; sketch its current shape and clear the work area.
Meeting 2 · 0–8 min

Predict and set up

  1. Revisit the two success checks. Agree on identical starting conditions and prepare a before/after results table.
Meeting 2 · 8–23 min

Collect evidence

  1. Open and close the latch five times. Record catching, tearing or accidental opening.
  2. One student operates while the other records. Swap for a later trial while noting a change of operator if it affects the result.
Meeting 2 · 23–35 min

Change one thing

  1. Change one loop gap or bar width. Repeat the same five cycles without forcing it.
  2. Keep the original results rather than replacing them with only the best attempt.
Meeting 2 · 35–45 min

Explain and clean up

  1. Show the model door and labeled sliding parts with your cycle results.
  2. Collect the brief and results; separate reusable materials and clean the test area.

Assessment

  • Latches and unlatches by hand
  • Door swings freely when unlatched
  • Student demonstrates the actual task: Open and close the latch five times. Record catching, tearing or accidental opening.
  • Record includes failures as well as successes.
  • Student identifies one changed feature and uses the retest to explain the result.

Supports & extensions

  • Provide fold marks or pre-cut parts; accept drawings or dictated observations.
  • Start with the smallest working version of model door latch before decoration.
  • Extension after success: choose one more value for the same tested feature, predict its effect and repeat open and close the latch five times.

Safety & responsible use

  • Teacher checks materials and test conditions before use. Use classroom scissors; adults prepare difficult cuts, holes and fasteners.
  • No powered tools, coding, hot glue or electrical circuits are required. Keep moving objects contained and test loads light.
  • Keep pieces on the tabletop, do not mouth materials and stop if a part tears into a sharp or loose hazard.

No-machine alternative

Use prepared paper parts, larger pieces or an adult-assisted version of the same build. Keep the functional task: Make a cardboard door with a sliding latch that a partner can open and close. If physical testing is not possible, label sketches as predictions rather than measured results.

Printable student design brief

The challenge

Make a cardboard door with a sliding latch that a partner can open and close.

Success criteria

  • Latches and unlatches by hand
  • Door swings freely when unlatched
  • Record the stated test and explain one revision

Constraints

  • Use only the listed teacher-approved materials
  • Stay within the teacher-set size, load and test-space limits
  • Two 45-minute meetings; keep the first version simple

Engineer’s notes

Who uses this object, and what should it do?
Draw two possible designs. Label the working parts and circle your choice.
Which size, fold, gap or position must you measure or mark?
Before testing, predict what will happen: Open and close the latch five times. Record catching, tearing or accidental opening.
Record each trial: condition / expected result / actual result.
Draw the ONE change you made. What stayed the same?
Record the retest. Did the change help, not help, or leave the result uncertain?
Show and explain: one result that supports your conclusion.
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