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EthicsMiddle schoolKey Stage 3

How to teach the trolley problem

The trolley problem asks whether you would switch a runaway trolley away from five people onto a track with one, and the footbridge case asks whether you would push one person to stop it. This page explains both, with a free activity where students pull a track switch Sparky builds and test their own rule as Sparky changes one detail at a time.

Jemel Fanfan

Jemel Fanfan | Founding Member at Flint

Title card reading 'How to teach the trolley problem', next to three chat cards: a student says five is more than one so always pull the lever, Sparky asks whether he would push in the footbridge case, and he says pushing would use the man to block the trolley.

"It was interesting how even if the students attempted to not take the program seriously, Flint forced students to answer the prompts in a way that focused on the question."

Rebekah RingRebekah Ring, Executive Functioning Skills Teacher at Ravenscroft School

Why this matters

Many middle schoolers answer the trolley problem in one line: five is more than one, so pull the lever. A worksheet records that answer and moves on, so the student never meets a case where the numbers stay the same and their own answer changes. The teacher has to wait for the class discussion to find out who can say why pushing a person feels different from pulling a lever.

The trolley problem and the footbridge case

Philippa Foot described the first version in 1967: the driver of a runaway trolley can steer it away from five people on the track ahead onto a side track where one person stands (Stanford Encyclopedia of Philosophy; Thomson, 1985). Judith Jarvis Thomson gave the puzzle its name, and in her 1985 paper "The Trolley Problem" she moved the choice to a bystander at a switch and added a footbridge case, where the only way to stop the trolley is to push a heavy stranger off a bridge into its path (Yale Law Journal).

Both cases trade one life for five, yet many people believe pulling the switch is allowed and pushing the stranger is wrong (Stanford Encyclopedia of Philosophy). The pair tests whether only the numbers matter, or also how the harm happens: whether the one person's death is a side effect of saving the five or the means of saving them.

In the Flint activity, each student pulls a track switch Sparky builds and states a rule for the choice. Unlike a worksheet, Sparky then changes one detail, builds the new version of the track in that student's chat, and asks whether the student's own rule still holds.

Sparky gets Omar to test his rule until he finds why pushing is different

Omar starts with "five is more than one" and ends up explaining why pushing a stranger is different from pulling a lever. Every student gets the same activity and the same cases in the same order, and Sparky's replies and new tracks depend on the rule each student states.

Sparky changes one detail and builds a new trackSparky sends Omar back to his own ruleA clear reason gets a harder question
O

Omar

Interest: Video game strategyStarting point: Five is more than one, so always pull the lever

Omar

i flipped the lever to the side track. five is more than one, so always pull the lever. its like in strategy games, you lose 1 unit to save 5 thats just a good trade

Sparky

So your rule is: always choose the option that saves the most people. Now let's change one detail. What if the one person on the side track is your best friend, and the five on the main track are strangers you've never met? Does your rule still hold here?
An interactive Sparky made in the chat, titled Trolley Problem: Your Friend vs. 5 Strangers. A yellow trolley rolls along a blue main track toward five stick figures labeled 5 Strangers. A lever sits by the switch, and a gray side track curves down to one stick figure labeled Your Friend. Under the drawing are two buttons, Go toward 5 Strangers and Go toward Your Friend, a note that reads: The trolley goes toward 5 Strangers. It stops before reaching them, and a Confirm my choice button.
InteractiveTrolley Problem: Your Friend vs. 5 Strangers

Omar

friends are just an exception i guess. so five is more than one, always pull, unless its someone you know

Sparky

So your rule is: save the most people, unless one of them is someone you know. Now here's a new version, no lever this time. There's a footbridge above the track, and a stranger is standing on it. The only way to stop the trolley from hitting the 5 strangers is to push that stranger off the bridge onto the track. By your rule (save the most people, and both are strangers), you should push. Do you?
An interactive Sparky made in the chat, titled Trolley Problem: Footbridge Variation. The text says the only way to stop the trolley heading toward 5 strangers is to push the 1 stranger on the bridge onto the track. The drawing shows an orange trolley on the left, a footbridge with one figure labeled 1 Stranger standing on top, and five figures labeled 5 Strangers on the track past the bridge. A note says the buttons are choices to think about, not instructions to do anything in real life. Below are three buttons: Push, Don't Push and Pause.
InteractiveTrolley Problem: Footbridge Variation

Omar

no i wouldnt push him. thats different

Sparky

You said your rule was "save the most people, unless one of them is someone you know," but both groups here are strangers, just like the original. So what makes this feel different to you?

Omar

with the lever the trolley just goes a different way and the guy happens to be on that track. but if i push him im using him to block it, like using a unit as a shield. its still 5 vs 1 tho so idk

Understanding check

You're saying redirecting harm feels different from using someone as a tool to stop it, even when the numbers are the same. Philosophers have a name for that idea: the means vs. side effect distinction. If the outcome is identical, why does how it happens matter morally?

Found that his rule left out how the harm happens

Omar is an example student. Sparky's replies are shortened, and one exchange about the friend case is left out.

What Flint did for Omar

  • When Omar said five is more than one, Sparky built a new track with his best friend on the side track.
  • When Omar refused to push in the footbridge case, Sparky quoted his own rule back to him and asked what was different.
  • When Omar said pushing uses the man to block the trolley, Sparky named the idea and asked why how it happens matters.

A teacher can't do this by hand for 30 students, and Sparky does it in every student's chat.

The activity page shows who is still only counting the numbers

While the class works, Needs attention shows the teacher which student is stuck and on which message. After three or more students submit, activity analytics lists what the class explained well, where students went wrong, and a follow-up to practice next.

Flint's activity page for the trolley problem activity. Needs attention shows that one student answered all three cases with '5 is more than 1' and hasn't said why pushing feels different from pulling. Activity analytics says most students stated a rule for the lever case, and 16 students explained the footbridge as using a person to stop the trolley. 9 students called the friend case an exception without saying why. The follow-up suggests trying the loop track and testing whether the new rule still holds. The Sessions table lists three students: two submitted and one still in progress.

Example activity page

After a middle school ethics class tests its rules on the trolley problem

The school and students are made up for this page.

Set up the activity for free

Open the trolley problem activity in Flint's public library, select Use activity to copy it into a free Flint account, and assign it to a class. Sparky builds the track switch and each new version of it inside the student's chat, with no setting to turn on. The activity's guidelines for Sparky list the cases in order, so you can add or swap a case by editing that list.

For more ethics activities, see Flint for ethics.

Start the activity for free

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