IGCSE Maths Textbooks

[xing]

I would like to teach DS IGCSE Maths at home, can anyone recommend a good textbook? And how to register him to take the test in a school as an external candidate?

Is there any particular reason for IGCSE rather than GCSE? Last year dd did Edexcel GCSE and did the exam at a local school which was doing the same exam. We used the Letts revision guides and workbooks, with Khan Academy to dip into to explain the more difficult bits. Nearer the exam we used "GCSE To A* in a Week" ro revise, and the past papers from the Edexcel website. It is really worth going through the mark scheme to learn the stock phrases which come up year after year in the answers.
To register, you have to phone round schools to find one which will take external candidates, then go in to fill in a form and pay the entrance fee and their admin fee. Last year this came to about £55.

JustRichmal, thank for the advise. I shall check with the school and go with the exam board that the school uses. BTW, DS likes Khan Academy as well.