The Irish settlers mainly settled in the west of Scotland, not far from where the boats landed, which is why eg Ayrshire, where I am from, is particularly sectarian. Migration from Ireland had a huge effect on the communities in Ayrshire - we can see parallels today.
My great, great grandmother's family came to Ayrshire from Ireland. The men worked in the quarries and the women in the thread mill.
Those who came over were often the poorest of those leaving Ireland - if you had the money you were more likely to go to America or Canada.
There was so much antagonism towards the newcomers, which turned into antagonism to Catholics. Where I lived, Catholics were discriminated against jobs wise and mostly couldn't find well paid work. For example, my mum worked as a secretary at a thread mill. Catholics could work on the shop floor but not in the office.
I live in England now. There are Catholic schools here too. The difference is that Catholics were not discriminated against to the same extent.