Algorithms and Scratch Models
Grade 7 | Computer Science | Unit 02
Teacher's Guide
Learning objectives
- Explain the central ideas of algorithms and scratch models using appropriate vocabulary.
- Apply the worked example and justify answers to the practice questions.
- Complete the investigation or design task and identify a limitation of its model or evidence.
Prerequisites: Basic reading, arithmetic, and step-by-step reasoning.
Suggested time: Two or three 45-minute sessions; extend the activity when needed.
Teaching sequence
- Elicit a prior explanation of the topic and note uncertain vocabulary.
- Discuss the concept section, distinguishing observations, models, and assumptions.
- Work through the example. Ask students to explain each step and check any units.
- Complete the activity, then use the five practice questions as an individual check.
- Review the two vocabulary questions and revisit misconceptions revealed by the answers.
Assessment and differentiation
Use the seven questions in the companion CSV for retrieval practice or a short quiz. Award one point per entry for an accurate answer; accept scientifically equivalent wording. Treat five correct answers as a suggested checkpoint for further review, with both reasoning and activity quality assessed separately. Support students with a labeled diagram, a word bank, or a completed first step. Extend by asking students to change one example condition, predict the effect, and explain a limitation.
Student Worksheet
Concept and helping material
An algorithm is a clear sequence of steps for completing a task. Computational thinking includes decomposition, finding patterns, and selecting important details. A program expresses an algorithm in a language a computer can execute. In a block-based environment such as Scratch, events start scripts and blocks define actions. The sequence matters because later actions depend on earlier state. A model or animation can demonstrate scientific ideas, but its behavior follows the rules written by the programmer. Testing a model requires checking both the code and the scientific assumptions.
Vocabulary
- Algorithm: A defined sequence of steps for solving a problem or completing a task.
- Decomposition: Breaking a problem into smaller manageable parts.
Worked example
A square-drawing algorithm repeats move 50 steps and turn 90 degrees four times. Repeating three times leaves the square incomplete; using a different turn angle changes the shape.
Investigation or design task
Draw a flowchart and write block-style pseudocode for a square. Predict output before using an optional teacher-approved coding environment.
Practice
- How many 90-degree turns complete the square algorithm?
- Why does instruction order matter?
- What is an event in an interactive program?
- Does a correct animation prove the scientific model is accurate?
- What is one benefit of a flowchart?
Vocabulary retrieval
- Define Algorithm.
- Define Decomposition.
Reflection
Explain which evidence, calculation, or model supports one of your answers. State a condition under which your explanation might need revision.
Answer Key
- Four.
- Each instruction acts on the state produced by earlier instructions.
- An action or signal that triggers a response or script.
- No. Code can correctly implement unrealistic assumptions.
- It makes the sequence and decisions easier to inspect.
Vocabulary definitions appear above and are also included in the CSV. Activity answers may vary; require a clear method or design, correct use of lesson concepts, and an explicit limitation. Reflection is assessed for reasoning rather than one fixed phrase.
Source Reference
Everything You Need to Ace Computer Science and Coding in One Big Fat Notebook, PDF viewer pages 121-158,211-257 (1-based). Page numbers refer to this supplied file and may differ from printed page numbers. The source is background reading for the grouped topic. Lesson explanations, examples, and questions are original teaching material; they do not reproduce the book's worksheets or illustrations.