Re the comment about GCSE and IGCSE being different: GCSE and IGCSE are very different exams with different target markets. GCSE is an exam in England (and Wales, tho with differences); IGCSE is aimed at international candidates. Coursework is no longer included in non-practical GCSEs but is allowed in IGCSEs which may be why some private schools choose IGCSE (not an option for state schools in England).
The exams for MFL (my subject) as an example are so different. The IGCSE written exams are all in the target language (all questions and answers) while a lot of the GCSE paper is in English (so you need to know what the TL words mean!); there is also translation in GCSE but not in IGCSE for obvious reasons. Grammar task in IGCSE but not in GCSE.
The speaking specs are very different as well. AQA and Edexcel GCSE are actually very similar; but yes, Edexcel GCSE and Edexcel IGCSE are very different. For Edexcel IGCSE the candidate chooses a picture in advance and can prep answers to the likely questions on that; they are also questioned on two other topics chosen by a grid. For Edexcel GCSE the candidate chooses one topic and speaks for 1 min and then has questions on that and one other topic; they also prep (on the day) a previously unseen roleplay and photocard chosen by the exam board via a grid. Very similar to AQA GCSE, but Edexcel GCSE/IGCSE not similar at all apart from the topics covered.
I imagine there are similar variations in structure and form of the exam with other subjects. Maybe it’s more obvious in MFL bc of the translation aspect and questions all in TL.
This of course underlines the importance of the candidate knowing and understanding the spec for each subject and the different boards. I do a lot of speaking assessments for two MFL, all boards and specs (14 different specs this year!) and I’m astonished every year that while some candidates are very well prepped, some will come into the speaking exam room without any clear idea of what the assessment will entail. I asked one candidate last year (as I am supposed to) if they had any questions for me (they need to ask me two for AQA A level) and they said, in excellent German, “no, not really.” Arrrgh.