Module 3: Step-by-Step Thinking -- Study Guide
Lesson 1: What is Decomposition?
Decomposition means breaking a big task into smaller, easier pieces. Instead of doing one huge thing, you do a bunch of small things, one at a time.
Why Decomposition Helps
- Big tasks can feel scary or impossible
- Small steps are easy to understand and do
- You can always break a step down further if it still feels too big
- Coders, doctors, chefs, and builders all use decomposition
Example: "Clean your room" breaks down into: pick up clothes, put books on shelf, put toys in bin, make bed, put dishes in sink, check under bed.
Key idea: Every big task is really just a bunch of small tasks put together.
Lesson 2: Writing Clear Instructions
Sequencing means putting steps in the right order. When you write instructions, you have to think about which step comes first, second, and so on.
Four Rules for Great Instructions
| Rule | What It Means |
|---|
| Start at the beginning | Do not skip the first steps |
| One action per step | Each step tells you to do just one thing |
| Put steps in order | Think about what needs to happen first |
| Be specific | Say exactly what to do, not a vague description |
Common Problems
- Steps out of order: Doing things in the wrong sequence causes mistakes
- Missing steps: Leaving out important steps causes confusion
Key idea: Computers follow instructions exactly. They cannot guess what you meant, so every step must be clear and in the right order.
Lesson 3: Recipes and Directions
Three Ways to Show Steps
| Format | What It Is | Best For |
|---|
| Numbered list | Steps written as 1, 2, 3... | Simple instructions |
| Recipe | Ingredients plus numbered steps | Cooking, crafts, experiments |
| Flowchart | Boxes and arrows showing order | Seeing the whole plan at a glance |
Flowchart -- A diagram that shows steps in order. It uses boxes to hold each step and arrows to connect them. You read it by following the arrows from start to finish.
Key idea: Coders often draw flowcharts to plan their programs before writing any code.
Lesson 4: Sequencing in Scratch
Sequence (in coding) -- A set of instructions that run in order, one after the other, from top to bottom.
Important Scratch Blocks
| Block | What It Does |
|---|
| when green flag clicked | Starts the program when you click the green flag |
| say [text] for (2) seconds | Makes the sprite show a speech bubble with text |
| wait (1) seconds | Pauses the program for a moment |
| move (10) steps | Moves the sprite forward |
| turn right (15) degrees | Turns the sprite to the right |
| pen down | Makes the sprite draw a line as it moves |
| pen up | Stops the sprite from drawing |
| switch costume | Changes how the sprite looks |
Drawing Shapes
| Shape | Sides | Turn Degrees |
|---|
| Triangle | 3 | 120 |
| Square | 4 | 90 |
| Pentagon | 5 | 72 |
| Hexagon | 6 | 60 |
Key idea: A stack of Scratch blocks is just a set of clear, ordered instructions -- the same skill you have been practicing all module!
Big Ideas to Remember
- Decomposition = breaking big things into small steps
- Sequencing = putting steps in the right order
- Clear instructions = one action per step, specific, complete
- Flowcharts = pictures that show steps with boxes and arrows
- Scratch sequences = blocks snapped together, running top to bottom
- Order matters in recipes, directions, flowcharts, and code