Introduction to Algorithms: Step-by-Step Solutions — Free K-12 lesson plan

Lesson plan

Objectives

Students will be able to define an algorithm as a set of ordered instructions.
Students will be able to identify examples of algorithms in everyday activities.
Students will be able to create a simple, sequential algorithm to solve a given problem.
Students will be able to accurately follow a set of instructions (an algorithm) to complete a task.

Materials

Whiteboard or projector
Markers or pens
Student notebooks or blank paper
Pencils
Algorithm Challenge Cards (pre-printed cards with simple tasks like 'Sharpen a pencil', 'Get a book from a shelf', 'Make a peanut butter sandwich')
Construction paper or drawing paper for 'Algorithm Drawing Game'
Index cards for exit tickets
Optional: Large open space for 'Human Robot Challenge'

Warm-up

Begin by asking students: 'What are the steps you take when you get ready for school in the morning?' or 'How do you make a sandwich?' Have them share a few steps out loud. Explain that these are like 'recipes' for doing things. Introduce the idea that computers also need 'recipes' to do tasks, and these recipes have a special name.

Direct instruction

**Introduce Algorithms:** Write 'Algorithm' on the board. Explain that an algorithm is a set of clear, step-by-step instructions for solving a problem or completing a task. It's like a recipe, but for anything, not just food!
**Everyday Examples:** Ask students for examples of things they do every day that have steps. Guide them to think of things like brushing teeth, tying shoes, making a bed, or getting a drink of water. Emphasize that these are all algorithms because they follow a specific order.
**Key Characteristics:** Discuss that algorithms need to be: 1) Clear (easy to understand), 2) Sequential (steps in order), and 3) Complete (all necessary steps included). Use the 'brushing teeth' example to show what happens if steps are out of order or missing.
**Simple Algorithm Demonstration:** As a class, let's create an algorithm for 'How to draw a square'. Write down each step as students suggest it: '1. Get a piece of paper. 2. Get a pencil. 3. Draw a straight line across. 4. Draw a straight line down from the end of the first line. 5. Draw another straight line across to connect to the starting point. 6. Draw a straight line up to connect the two lines.'
**Importance of Order:** Discuss why the order of steps is so important. What if we tried to draw the lines before getting paper and pencil? What if we tried to connect lines that weren't drawn yet? This reinforces the 'sequential' characteristic.
**Analogy to Computers:** Explain that computers use algorithms all the time. When you play a game, type a letter, or search for something online, a computer is following a very complex algorithm. We are learning the basics of how computers 'think'!
**Introduce Pseudocode (Simplified):** Explain that programmers write algorithms using 'code,' but we can use plain English to write our steps. This is sometimes called 'pseudocode' – it looks like code but is easy for humans to read. We'll just write numbered steps.
**Review and Q&A:** Briefly review the definition and characteristics of an algorithm. Answer any questions students have before moving to practice.

Guided practice

Divide the class into small groups (3-4 students). Introduce the 'Human Robot Challenge'. One student in each group will be the 'robot' (blindfolded or eyes closed, if safe and practical, or just instructed not to move without instructions), and the others are the 'programmers'. The programmers must write a simple algorithm (a sequence of steps) to guide their 'robot' across a designated area in the classroom (e.g., from their desk to the whiteboard, avoiding an imaginary obstacle). Emphasize using clear, precise instructions like 'Take 3 steps forward', 'Turn right 90 degrees', 'Take 2 steps backward'. After writing, one group can demonstrate their algorithm with the teacher acting as the 'robot' following their exact instructions. For example, a group might write: '1. Take 4 steps forward. 2. Turn left. 3. Take 2 steps forward. 4. Stop.' The teacher would then execute these steps precisely.

Independent practice

Distribute 'Algorithm Challenge Cards' to each student or pair of students. Each card will have a simple task (e.g., 'Sharpen a pencil', 'Get a book from the shelf', 'Put on a jacket'). Students will choose one card and, in their notebooks, write down a clear, step-by-step algorithm to complete that task. Remind them to think about every single small step and put them in the correct order. Encourage them to be as precise as possible, imagining they are writing instructions for a robot. Circulate to provide support and check for understanding, ensuring steps are sequential and clear.

Closure

Bring the class back together. Ask a few students to share an algorithm they wrote for their challenge card. Discuss any challenges they faced in making their instructions clear and sequential. Conclude by reiterating that algorithms are everywhere and are essential for computers to work. For an exit ticket, have students write on an index card: 'What is one new thing you learned about algorithms today?' or 'Write the first two steps of an algorithm to make a paper airplane.' Collect the cards as students leave.

Assessment

Mastery will be assessed through: 1) Observation of student participation and understanding during the 'Human Robot Challenge' and class discussions. 2) Review of the algorithms written during independent practice for clarity, sequential order, and completeness. 3) Analysis of student responses on the exit tickets to gauge their grasp of the core concept. 4) Performance on the end-of-lesson quiz.

Differentiation

For struggling learners, provide pre-numbered steps for the 'Human Robot Challenge' or 'Algorithm Challenge Cards' and ask them to fill in the missing actions, or provide a word bank of action verbs. Pair them with a stronger peer. For advanced learners, challenge them to create an algorithm for a more complex task, such as 'How to play a simple game' or 'How to make a simple drawing (e.g., a house)', or ask them to 'debug' a faulty algorithm by identifying missing or out-of-order steps.

Algorithm Adventures: Step-by-Step Fun!

An algorithm is a set of clear, step-by-step instructions to solve a problem or complete a task. Think like a computer! Read each problem carefully and write down the steps of the algorithm. Make sure your steps are in the correct order and easy to understand.

You want to make a glass of orange juice. List the steps in order.
You need to sharpen your pencil. Write the algorithm.
Imagine you are a robot. Write the steps to walk from your classroom door to your desk.
Put these steps in the correct order to brush your teeth: - Rinse your mouth with water. - Put toothpaste on your toothbrush. - Brush your teeth. - Get your toothbrush wet. - Turn on the water.
Write an algorithm for how to make a simple paper airplane.
What would happen if you forgot step 3 in your 'make a glass of orange juice' algorithm (opening the carton)?
You want to draw a smiley face. Write the algorithm.
Imagine you are making toast. These steps are out of order. Rewrite them correctly: - Put bread in toaster. - Get a slice of bread. - Eat the toast. - Press the lever down. - Take toast out of toaster.
Write the algorithm for how to get ready for bed.
Why is it important for an algorithm to have clear steps?
What is one task you do every day that is like an algorithm?

Algorithm Check-Up

What is an algorithm?
- A type of computer game
- A set of clear, step-by-step instructions
- A secret code
- A very fast calculation
Answer: A set of clear, step-by-step instructions
Which of these is an example of an algorithm?
- Watching a movie
- Daydreaming
- Following a recipe to bake cookies
- Listening to music
Answer: Following a recipe to bake cookies
Why is the order of steps important in an algorithm?
- It makes the algorithm look nicer.
- It doesn't matter, you can do steps in any order.
- Doing steps out of order might lead to the wrong result or not work at all.
- Computers only understand numbers.
Answer: Doing steps out of order might lead to the wrong result or not work at all.
Which word best describes the steps in an algorithm?
- Confusing
- Random
- Sequential
- Messy
Answer: Sequential
If you are writing an algorithm for 'How to make a sandwich,' what would be the FIRST step?
- Put on the top slice of bread.
- Get two slices of bread.
- Spread peanut butter.
- Eat the sandwich.
Answer: Get two slices of bread.
What happens if a step is missing from an algorithm?
- The algorithm will still work perfectly.
- The task might not be completed correctly or at all.
- The computer will guess the missing step.
- It makes the algorithm faster.
Answer: The task might not be completed correctly or at all.
True or False: Only computers use algorithms.
- True
- False
Answer: False
Which of these is NOT a characteristic of a good algorithm?
- Clear steps
- Sequential steps
- Steps that are difficult to understand
- Complete steps
Answer: Steps that are difficult to understand

Algorithms at Home!

Dear Parents/Guardians, This week in Computer Science, your child learned about algorithms. An algorithm is simply a set of clear, step-by-step instructions to solve a problem or complete a task. We discussed how recipes, getting ready for school, or even playing a game all involve algorithms. Computers rely on algorithms for everything they do! This homework encourages your child to look for algorithms in their daily life and practice creating their own instructions. Please encourage them to think carefully about each step and its order.

**Algorithm Detective:** Find one task you do at home every day (e.g., making your bed, feeding a pet, setting the table) and write down the algorithm (all the steps in order) in your notebook. Be very specific!
**Family Algorithm:** With a family member, choose a simple chore (like washing dishes or taking out the trash). Work together to write down the algorithm for that chore. Make sure every step is included.
**Instruction Challenge:** Teach a family member how to do something new using only your step-by-step instructions. It could be how to draw a simple shape, how to fold a towel, or how to play a very simple game. See if they can follow your algorithm!
**Design an Algorithm:** Think of a simple game you like to play. Write down the algorithm for how to play the first few turns of that game (e.g., 'Player 1 rolls dice,' 'Player 1 moves piece').
**Algorithm Drawing:** On a blank piece of paper, draw a simple picture (like a house, a tree, or a stick figure). Then, on another piece of paper, write down the algorithm (step-by-step instructions) for how someone else could draw that exact same picture.
**Computer Connection:** Think about how a computer might use an algorithm when you search for a video on YouTube or play a game on a tablet. Write one sentence about what the computer's algorithm might be doing.
**Missing Step:** Imagine an algorithm for making a sandwich that forgot the step 'Put bread on plate'. How would that affect the final result? Write your answer.
**Creative Algorithm:** Invent a silly, short algorithm for something impossible, like 'How to make a cloud disappear' or 'How to teach a cat to sing'. Have fun with it, but still use clear, sequential steps!

Vocabulary

Algorithm · noun: A set of clear, step-by-step instructions for solving a problem or completing a task.; "The recipe for baking cookies is an algorithm for making a tasty treat."
Step · noun: One single action or instruction in an algorithm.; "The first step in our algorithm was to get a piece of paper."
Sequence · noun: The order in which things happen or are arranged.; "It's important to follow the correct sequence of steps when building with LEGOs."
Instruction · noun: A command or detailed information telling someone how to do something.; "The teacher gave clear instructions for the art project."
Problem · noun: A situation or task that needs to be solved or completed.; "The problem was how to get the ball off the roof."
Solution · noun: The answer to a problem or the way to fix something.; "Finding the right algorithm was the solution to making the robot move correctly."
Input · noun: Information or data that is put into a computer or system.; "When you type on a keyboard, your typing is an input to the computer."
Output · noun: The result or information that comes out of a computer or system after processing.; "The picture printed from the computer is an output."
Debug · verb: To find and fix errors or mistakes in an algorithm or computer program.; "We had to debug our algorithm because the robot kept turning the wrong way."
Program · noun: A set of instructions (an algorithm) written in a language that a computer can understand, telling it what to do.; "The computer program made the game work."
Computer · noun: An electronic device that can store, retrieve, and process data according to a program.; "My computer helps me do my homework and play games."
Code · noun: The instructions written for a computer, usually using a special programming language.; "Computer programmers write code to create apps and websites."

Activities

Warm-up: How-To Steps · 5 minutes
Students share the steps they take for a simple daily routine like 'getting ready for school' or 'making a sandwich'. The teacher writes down a few suggestions on the board, emphasizing the sequential nature of the steps. This activity activates prior knowledge and sets the stage for defining algorithms.
Guided Practice: Human Robot Challenge · 15 minutes
Divide students into small groups. One student acts as a 'robot' and the others are 'programmers'. Programmers write an algorithm to guide their robot through a simple path in the classroom (e.g., to a specific object). Emphasize precise, unambiguous instructions (e.g., 'Take 3 steps forward', 'Turn left 90 degrees'). Groups take turns demonstrating with the teacher as an example robot, following instructions exactly.
Independent Practice: Algorithm Challenge Cards · 10 minutes
Students receive 'Algorithm Challenge Cards' with simple tasks (e.g., 'Sharpen a pencil', 'Get a book from a shelf'). Individually or in pairs, they choose a card and write a detailed, step-by-step algorithm in their notebooks. The teacher circulates to offer support and check for clarity and correct sequencing of steps, reinforcing the lesson's key concepts.
Closure: Algorithm Charades · 5 minutes
To wrap up, the teacher or a student mimes a simple algorithm (e.g., brushing teeth, waving hello, making a phone call) without speaking. The class watches and tries to guess the algorithm being performed. This fun activity reinforces the idea that algorithms are sequences of actions and can be understood even without words, just like a computer follows instructions.
Bonus Activity: Algorithm Drawing Game · 10 minutes
Pair students up. One student draws a simple picture (e.g., a house, a flower) on one side of a paper. On the other side, they write an algorithm (step-by-step instructions) for how to draw that exact picture. Their partner then tries to draw the picture by *only* following the written algorithm, without seeing the original drawing. This highlights the importance of clear and precise instructions.