TA per class at least in my kids' infant school (but the Head intentionally does the budget to prioritise that over some other stuff - our IT is pretty crappy compared to a lot of schools as a result but does the job, just isn't new and shiny). Might not physically be "in" the class if they're doing interventions with other children, but there's one named and generally attached to each class.
Like someone else upthread I basically go in voluntarily a lot and work as an extra TA (I'm a primary teacher myself by trade) to free up the yeargroup TAs a bit as well.
The kids all do get heard read at least once a week in-school - either by a teacher, TA or an adult volunteer (there are a few of the school's ex-TAs who drop by and get handed the reading folder and told to get on with it as well!)
My Y2 child seems to be being heard read twice a week in school at the moment - once by a volunteer and once by either the teacher or TA - and she's really a kid who they could drop off that if time was running short (they know this - I'm not a parent who'll fuss, I'm one who keeps on at the reading at home and DD1 is a really confident reader), Y1 child gets heard once a week.
Teachers also make a point of highlighting kids they haven't listened to themselves in a while and targeting them specifically to hear as well in case they're in a place on the list where they tend to get heard by different volunteers most weeks.
I do supply though and we tend to get an attack of the disappearing TAs at times when the class TA suddenly develops the need to do all the other random jobs around school and vanishes for the day leaving you on your own!