Two seats are open on the student council. Four people are standing. You mark 1 for your first choice and 2 for your second. Today you watch how those numbers become seats, one round at a time, the way Irish elections are counted.

A preference is the order you put on the ballot: 1 is who you want most, 2 is who you want if your first choice cannot use your vote.

A quota is the number of votes you need to win a seat. With 100 valid votes and 2 seats:

That is the single transferable vote (STV), the system used for Dáil, local and European elections in Ireland. You are about to run a small version of it.

Open the interactive. Four candidates, 100 ballots, two seats. Watch what happens when someone passes the quota, and what happens when the lowest is excluded. Notice whose second preference still has work to do. At each freeze, turn to your partner and say the answer aloud before the class shares.

Talk these through with your partner first, then share as a class. Nothing is typed or saved.

1. Whose second preference ended up mattering most, and how can you tell from the count?
2. If only first preferences had counted, who would have taken the two seats?
3. In one sentence, what does a second preference actually do in this system?

You can now:

• say what a preference and a quota are in an Irish election count
• follow a single transferable vote (STV) count round by round, including surplus and exclusion
• spot when a second preference decides a seat

Next time you will open on this STV outcome (Aoife and Cara) and count the same ballots another way, then compare what changes.