Yes, I see your point, nina but I think the cost in teacher time that janea describes is too "expensive". The approach that goldengirl describes seems like a much better and more efficient idea.
There is also the fact that most (?) kids nowadays will have been to a playgroup or nursery already by the time they are old enough to start school so they have some experience of being in the charge of someone like a teacher.
What do you think would go well with coasters like this?