A Scottish/Irish Traveller bought a plot of land opposite the high school where I worked and set it up as a site. It was originally an illegal site, but the council eventually gave it retrospective planning permission. That's happened with other plots of land in the area and there are another three council-owned sites that I can think of .
I can't speak for other parts of the country, of course, but there's certainly no barrier in our LA to Traveller children being able to stay in high school until the end of 6th Yr.
As I mentioned in a previous post there are also Traveller families choosing to stay in council houses while the men are on the road. However, they do tend to disappear at certain times during the term, notably in time to make the journey down south for Appleby.
When I was still working, we sometimes had families choosing to take the whole family to Ireland for a few months before coming back to Scotland. Accommodation was not a problem - the children had permanent addresses in the school records.
There was also the issue (not unique to Travellers) of families choosing to take the children out of school during term time in order to have holidays abroad. (They're not fined in Scotland.) We'd know because the kids would come back to school with pictures of them 'swimming with the dolphins in Florida', etc.
As with any of our pupils, we'd attempt to integrate our courses enough to allow any children who missed the SQA exam diet to achieve National 3 or 4 via the in-house assessments taken outside the SQA diet period.