For school concession card: http://www.transitlink.com.sg/ezlink_school.html
Main points under Usage:
- The concession card must be carried as proof of eligibility when traveling on the MRT/LRT/bus in order to enjoy travel concession. School uniforms do not prove students' eligibility for travel concession.
- If you are a concession card holder and intend to pay cash, please let the bus driver know. Then tap your concession card at the reader for verification of the cardís validity before you drop your cash into the farebox.
So legally speaking, because you did not show your ID, nor did you tap it on the reader for verification, the drivers (all 12 of them) have every right to request that you pay the full adult fare. Failure to do so would require them to request that you disembark at the point where the fare you paid allows you to travel until. This is actually the policy the bus companies give to their drivers.
The previous 11 were "eating snake" so to speak, in letting you travel more than you paid for, and this is a common attitude among drivers because when they follow company policy in booting people off the bus, they get complaints from the commuters (i.e. people like you). So they'll rather not, to avoid trouble, as long as the company does not find out (e.g. through having a ticket inspector on board). The 12th driver is merely doing his/her duty and following company policy in asking you to alight at the point where the fare paid allows you to travel until.
Naturally, whether he/she did so in a polite manner would depend on the CCTV footage.