In the UK, differentiation and integration aren't taught for GCSE maths (to ~16 year olds, last year of compulsory schooling) [1] but are for AS-level maths (to ~17 year olds) [2]
However, students select which AS-levels and A-levels they want to study; students can drop math entirely if they so wish. And some CS departments will accept such students, putting them through a high-speed remedial math course.
> They explained derivatives to us on the first year of UK university CS degree
That's done partly as a refresher for those who didn't do maths at A-level (so would be 2 years out of not doing maths at all) and to take into account some systems that don't teach it.
At least that was the case for my UK university CS degree.
However, students select which AS-levels and A-levels they want to study; students can drop math entirely if they so wish. And some CS departments will accept such students, putting them through a high-speed remedial math course.
[1] https://filestore.aqa.org.uk/resources/mathematics/specifica... [2] https://filestore.aqa.org.uk/resources/mathematics/specifica...