Scratch · Grade 3 · Guided practice
How to code this project
What you will make: Program one, two or three flashes to send three agreed classroom messages.
Optional on-screen pattern model. A hand-operated paper-circuit signal is also valid. These are invented classroom messages, not emergency signaling instructions.
Before you start
- Draw one signal sprite with bright On and dark Off costumes. Label what 1, 2 and 3 flashes mean on a separate paper key.
- Make a variable flashes for all sprites.
Opening and saving: Open the teacher-approved Scratch editor and select your sprite. The recipe is a block-by-block guide, not text to paste into Scratch. Build blocks with matching names and keep indented lines inside their enclosing blocks. Save through File → Save to your computer as an .sb3 file; no public sharing is required.
Build it one step at a time
- Build the script on the signal sprite. Ask is in Sensing; answer is the oval Sensing value.
- After set flashes to answer, the first if rejects every value except 1, 2 or 3. Nest two green or blocks to fit three comparisons.
- Put both costume changes and waits INSIDE repeat flashes.
- Click the flag; enter 2 and watch the full sequence. The question returns after a one-second rest.
- A partner chooses a message without telling the observer. The observer counts flashes and checks the paper key.
Your block recipe
when green flag clicked
switch costume to [Off]
forever
ask [Type 1, 2 or 3 flashes] and wait
set [flashes] to (answer)
if <<<(flashes) = (1)> or <(flashes) = (2)>> or <(flashes) = (3)>> then
repeat (flashes)
switch costume to [On]
wait (0.4) seconds
switch costume to [Off]
wait (0.4) seconds
else
say [Use 1, 2 or 3.] for (2) seconds
wait (1) secondsPredict, test and record
Write your name and date on the printed page. Run every test, note the actual result, and retest after one change.
| Try this input | Expected result | Actual result / retest |
|---|---|---|
| Enter 1, 2, then 3 in separate rounds | Exactly the requested flashes; finishes Off | ________________ |
| Enter 0 or 7 | Instruction appears; no flashes | ________________ |
| Partner decodes a hidden choice | Decoded message matches the key | ________________ |
If it does not work
- Only one flash? Both On and Off need to be inside repeat.
- No pause? Use wait blocks after both costumes.
Make one change
Change flash duration only; test whether another pair can still count and decode.
We changed __________. We predicted __________. Our test showed __________.
Teacher pacing: Use a 45-minute coding session: 5 minutes to predict, 10 to model a first working response, 20 for paired building, 7 for tests and 3 to save and explain. Continue in another meeting if setup or debugging takes longer; do not rush hardware checks.
Grade 3 support: Model one block at a time; partners alternate choosing blocks and explaining the result. Accept spoken or drawn test evidence.
Teacher learning resources
Preview resources before class. Follow this page’s specified reference build; another tutorial may use different hardware.
Print support: The lesson’s Print button includes this guide, recipe and test table.
For teachers
Engineering standards
This shows how the lesson connects to the national NGSS engineering standards and what student work you can collect.
3-5-ETS1-1
Teams define who needs the rescue signal station and set measurable performance, safety, material, and time limits.
What students show: User-centered problem statement with criteria and constraints.3-5-ETS1-2
Teams compare at least two circuit, code, or enclosure ideas against the success criteria.
What students show: Labeled system diagrams and a recorded design choice.3-5-ETS1-3
Teams run a repeatable test—ask viewers to identify randomized signals from the same distance—then change one variable and retest.
What students show: Test table, code or build revision, and evidence-based explanation.Materials
- Cardboard, paper, craft sticks, tape, reusable building pieces, and student-proposed materials
- Project platform: Paper circuits + vinyl cutter + optional coding
- Breadboard, paper-circuit supplies, or low-voltage power when needed
- handmade switches, tabs, or buttons input component or student-designed substitute
- LED, reflective, or coded light signals output component or student-designed substitute
- LEDs, resistors, jumper wires, copper tape, switches, and clips as needed
- Vinyl cutting materials for an optional case, sign, mount, or model
- Computer with approved coding or simulation tools when needed
- Planning sheet, ruler, and test-data table
Teacher preparation
- Build and test one possible reference solution without making it the required design.
- Prepare a basic-materials table plus optional electronics and fabrication stations.
- If coding is used, prepare a starter option for a physical signal sequence or optional event blocks; students may propose another workable control method.
- Prepare optional fabrication templates and a file rule beginning G3_08.
- Mark adult approval points before power-on and machine fabrication.
Step by step
How to teach it
Meet the user and define success
- Introduce the application: Help a model rescue crew send three clear messages when speech cannot be heard.
- Identify the user, need, criteria, and constraints.
- Draw a system map with input → code → output.
Build a first solution
- Choose basic, electronic, and fabricated materials based on the team's idea.
- Build with power disconnected whenever electronics are used.
- Complete an adult check, then troubleshoot one connection or physical feature at a time.
Create the behavior
- Create the first working control using a physical signal sequence or optional event blocks.
- Predict what one rule, connection, or code change will do before testing it.
- Make the system understandable with labels, diagrams, comments, or coding blocks.
Test and improve
- Use the same procedure each time: ask viewers to identify randomized signals from the same distance.
- Record at least three results.
- Change one code, circuit, or physical-design variable and retest.
Fabricate and present
- Design a vinyl cutting part that protects, mounts, or explains the electronics.
- Adult reviews and operates fabrication equipment where required.
- Connect the finished system and demonstrate how the evidence improved it.
Assessment
- Problem statement names a real user and measurable need.
- Circuit matches the team diagram and uses components safely.
- Program connects the intended input to the intended output.
- Test conditions remain consistent and include recorded evidence.
- Revision addresses a documented failure or user need.
Supports & extensions
- Use color-coded wires and a photograph of each breadboard step.
- Provide block coding or partially completed code with one change at a time.
- Assign roles: circuit builder, coder, tester, and recorder.
- Let students explain findings orally or with labeled diagrams.
- Extension: add a second sensor, output, data display, or operating mode.
Safety & responsible use
- Use only teacher-approved low-voltage classroom electronics; never connect projects to wall current.
- Disconnect power before changing wires or components.
- Use the correct resistor with every standard LED and stop immediately if a part becomes hot.
- An adult handles soldering, laser cutting, printer setup, blades, and final power approval.
- Keep liquids away from boards unless a sealed, teacher-approved sensor activity specifically requires them.
No-machine alternative
Build with cardboard, paper mechanisms, paper circuits, or a free on-screen simulator. Students may invent another safe way to model the same function, then compare ideas, test one variable, collect evidence, and revise.
Printable student design brief
The challenge
Create a working rescue signal station for this need: Help a model rescue crew send three clear messages when speech cannot be heard.
Success criteria
- Three messages look meaningfully different
- A new viewer can learn the key quickly
- Controls and symbols match correctly
Constraints
- No emergency claims or real distress use
- Solution may be electronic or use reflected light
- Includes a paper, drawn, or vinyl signal key