I read somewhere today it would be 13-16 weeks if the schools were to close.
My current thinking is they will stay open until Easter / Spring break. The Scottish exams are only two weeks after then, so May.
The English exams are June?
Depending on how the NHS is coping, they could go down the route of schools closing at Easter but not reopening other than for the Senior school years / exams.
My theory being the spreaders of diseases are the little kids, who's hygiene can be questionable, ie They don't wash hands properly, and are very touchy with each other.
Where the older kids should be more than capable of understanding they need to use tissues not sleeves, wash properly, not share drinks, or touch each other's food.
The government is going on the theory people need to build and immunity to it. And if you isolate everyone, it isn't going to disappear, so when isolation ends people will start spreading it again.