Substitute Lesson Plan: Sorting Networks

Objective

Students will learn that computers can solve problems faster by working on several parts of a task at the same time (parallel processing), and will experience this concept firsthand by acting as "numbers" moving through a human sorting network.

Materials

• Resource: Sorting Networks (CS Unplugged), including the chalked court diagram and the Photocopy Master cards
• Chalk (to mark the sorting network on the ground/court, if not already drawn)
• Two sets of six numbered cards (cut from the Photocopy Master, page 73)
• A stopwatch (for the variation activity)
• An open outdoor space or large indoor space (gym/court)

Warm-up (~5 min)

1. Gather students and explain: "Today we are going to become numbers being sorted by a computer!"
2. Ask students: "If you had six numbers in random order, how would you put them in order from smallest to largest?" Take a few quick answers.
3. Explain that computers can sort numbers faster by comparing several numbers at the same time instead of one at a time — that is what today's activity will show.

Main Activity (~25 min)

1. Set up the network: If not already marked, use chalk to draw the sorting network pattern from the resource on the court (a series of connected lines and circles/nodes).
2. Form groups: Organize students into groups of six. Explain that only one team uses the network at a time, so other groups will wait and watch.
3. Hand out cards: Give each team member one numbered card from the Photocopy Master set. Make sure the six numbers are in jumbled (mixed-up) order before starting.
4. Position students: Each team member stands in a square on the left-hand (IN) side of the court, holding their card.
5. Explain the rules:
6. Move along the chalked lines.
7. When you reach a circle (node), stop and wait for another team member to arrive at the same circle.
8. Compare your two cards. The person with the smaller number exits to the left. The person with the larger number exits to the right.
9. Continue moving and comparing at each circle you reach.
10. Run the first team through the network. Watch for errors — if a team makes a mistake, they must start again from the beginning.
11. Check the result: When the team reaches the far (OUT) side of the court, check whether their numbers are in the correct order from smallest to largest.
12. Rotate teams: Repeat with the second team using the second set of cards, and continue rotating until all students have had a turn (repeat if time and group size allow).
13. Reinforce the rule with an example: Remind students of the key rule at each node/circle: the smaller value always goes left, the larger value always goes right.

Wrap-up / Exit Ticket (~10 min)

Gather students back together and ask them to answer (aloud or on paper) the following questions:

1. In your own words, what is the rule for what happens at each circle (node) in the network?
2. Were you in the correct order when you reached the other end of the court?
3. Why might using a network like this help a computer sort numbers faster than comparing them one at a time?

(Teachers/subs can accept answers such as: "the smaller number goes left, the larger goes right"; and "because several comparisons can happen at the same time instead of one after another.")

If Time Remains

Introduce the stopwatch variation: Time how long it takes each team to move through the network from start to finish. Run two teams (one after another) and compare their times. Ask students: "Do you think a team could get faster with practice? Why might that be?"