League tables and GCSC versus IGCSE

[dizzydo]

Can someone please explain this to me and forgive my ignorance.

Do some private schools only take IGCSE's or do they mix and match depending on ability and how do they decide who will do which one?

TIA I know I will find my answer here

At dc's school they only do iGCSE for maths and only the top set do iGCSE, In other schools they may do more subjects for iGCSE and sometimes all the sets will do them - it may well be that at those schools where everyone does them, the children are all higher ability (ie tougher entrance criterea).

At my DSs' school, the top 30% (ish) do iGSCE maths.

what's the difference?

At Dh's school, iGCSE Maths is taken by all the students.