Is this common in Irish schools?
Yes, very. You're right, it's an Irish thing. In the last school where I taught, there was a retirement do for one of the teachers and as soon as the meal was over, the singing started. She opened the proceedings herself by singing 'Will You Go Lassie, Go?', you know that lovely Scottish song. Then everybody who wanted to, got up and sang, including the parents :) Some of them had had a good few jars by the time their turn came! After that we had a dance/disco.
Was yours a private or state school ?
It was what's called a voluntary school, privately owned and managed by the nuns and you pay whatever you can afford. There's no set fee. If you can't afford to pay anything, you don't pay. If you can afford to contribute, you do. The teacher's salaries are covered largely by the Department of Education and the school gets grants for certain things but we had to have many a fund-raising cake sale, or school concert :))
bizarre that primary children sing it!
I think the reason we liked it so much was that justice is seen to be done when the 'aul wan' is hung at the end. The 'choild' may have been 'kilt' but the 'aul wan' didn't get away with it :-D