Grade 3 · Low-Tech Builds · Lesson 73

String Phone

Make a two-cup string phone and compare how clearly a partner hears the same quiet message.

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

Your project in view

What you are making

Make a two-cup string phone and compare how clearly a partner hears the same quiet message.

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 String Phone: Make a two-cup string phone and compare how clearly a partner hears the same quiet message.
String Phone · Generated project example

Student directions · Grade 3

What will you make and do?

Make a two-cup string phone and compare how clearly a partner hears the same quiet message.

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 two cups linked by string. Predict whether a loose or gently taut string will carry the message better.

  2. 2Make the first parts

    Thread the string through adult-prepared holes and secure its ends inside the cups with the teacher’s method.

  3. 3Put it together

    Stand at marked spots so the string is gently taut without crossing a walkway. One partner speaks quietly and one listens.

  4. 4Test it fairly

    Try the same short message three times with taut string and then loose string. Record the words heard.

  5. 5Improve one part

    Change one connection if the string slips. Repeat without changing distance or speaking volume.

  6. 6Show and turn in

    Show the phone and compare heard-word records. Explain the role of the vibrating cup and string.

How will you know it works?

  • String stays securely attached
  • Partner can compare the same message under both string conditions
  • 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 two-cup string phone and compare how clearly a partner hears the same quiet message. 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: String stays securely attached; Partner can compare the same message under both string conditions.

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: Try the same short message three times with taut string and then loose string. Record the words heard. Change one connection if the string slips. Repeat without changing distance or speaking volume.

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

Materials

  • Two paper cups with adult-made holes
  • cotton string
  • tape
  • message cards
  • Pencil, planning paper and the printable design brief below

Teacher preparation

  1. Gather per-pair materials: Two paper cups with adult-made holes; cotton string; tape; message cards.
  2. Make one rough sample and rehearse the exact test: Try the same short message three times with taut string and then loose string. Record the words heard.
  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 two-cup string phone and compare how clearly a partner hears the same quiet message.
  2. Draw two cups linked by string. Predict whether a loose or gently taut string will carry the message better.
  3. Students say what would count as a successful result.
Meeting 1 · 8–18 min

Model the unfamiliar action

  1. Demonstrate slowly: Thread the string through adult-prepared holes and secure its ends inside the cups with the teacher’s method.
  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. Stand at marked spots so the string is gently taut without crossing a walkway. One partner speaks quietly and one listens.
  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. Try the same short message three times with taut string and then loose string. Record the words heard.
  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 connection if the string slips. Repeat without changing distance or speaking volume.
  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 phone and compare heard-word records. Explain the role of the vibrating cup and string.
  2. Collect the brief and results; separate reusable materials and clean the test area.

Assessment

  • String stays securely attached
  • Partner can compare the same message under both string conditions
  • Student demonstrates the actual task: Try the same short message three times with taut string and then loose string. Record the words heard.
  • 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 string phone before decoration.
  • Extension after success: choose one more value for the same tested feature, predict its effect and repeat try the same short message three times with taut string and then loose string.

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.
  • Never wrap string around a body part or pull hard. Keep string below face level and out of walkways.

No-machine alternative

Use prepared paper parts, larger pieces or an adult-assisted version of the same build. Keep the functional task: Make a two-cup string phone and compare how clearly a partner hears the same quiet message. If physical testing is not possible, label sketches as predictions rather than measured results.

Printable student design brief

The challenge

Make a two-cup string phone and compare how clearly a partner hears the same quiet message.

Success criteria

  • String stays securely attached
  • Partner can compare the same message under both string conditions
  • 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: Try the same short message three times with taut string and then loose string. Record the words heard.
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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