Computational Thinking Lesson Plan: Pixel Picture Algorithms

Lesson Procedure:

1. Project the BrainPOP movie Computational Thinking on the whiteboard. Read aloud, or have a volunteer read the summary of the movie that appears under the player.     
2. Show the Computational Thinking movie to the whole class. Turn on the closed caption option to aid in comprehension.
3. After the movie, draw attention to the Computational Thinking posters displayed (see Preparation) in the classroom. Tell students that today’s activity will focus on the algorithm design step of the computational thinking process. Review that algorithm design is creating a list of steps or instructions. Point out that in coding, it's the part when you actually write out the program.
4. Display Pixel Picture 1. Explain that today they will think like coders or computer programmers, and use algorithms to create pixel pictures, like this one. Remind students that a pixel is one point in a computer-generated image.
5. Distribute grid paper and markers to all students. Instruct them to make a picture using four colors. It’s okay to have white blocks--they do not need to fill every one. Lastly, tell them to KEEP THEIR PICTURE A SECRET! Point out that Moby is an example, but they should design something else. Encourage them to take risks and try something unusual. Make more grid paper available for them to start over if need be.
6. Once everyone has completed their pictures, instruct students to number the rows 1-12; they can also label the columns (across top) but it’s not necessary.
7. Display Pixel Picture 2 and direct students’ attention to the instructions or algorithm on the left. Read through the first few rows. Ask students what this is an algorithm for. They should recognize that they’re instructions for how to make the pixel picture of Moby.
8. Distribute the Algorithm Sheet, and have students write the algorithm for their picture, giving instructions row by row. Remind them to keep their pictures and algorithm a secret.
9. Next, pair students and assign one student in the pair to the job of programmer and the other computer. (Note, they will swap later). The programmer reads their algorithm aloud to their partner, the computer. The computer creates the pixel picture as directed. When they reach the end of the algorithm, compare the original picture with the new one. If there was a difference between the two, encourage the pair to work together to debug the algorithm.
10. Have students swap roles, so the programmer becomes the computer. Repeat the activity.
11. Finally, bring the class together and reflect on the experience. Discuss the importance of giving clear directions. Have students explain why their direction were or weren’t clear and if the latter, how they could have improved them.