IB students frequently need an SAT score for American applications, and the two loads can be carried together if the sequencing is deliberate.
Why the order matters
IB deadlines are fixed and numerous: internal assessments, the extended essay, theory of knowledge, mocks. They cannot be moved.
SAT dates can be chosen. So the calendar is built in one direction only: IB commitments first, then the SAT placed into a genuinely free window.
Doing it the other way round produces an SAT date sitting on top of two internal assessment deadlines.
The best window
Usually the end of the first year or the start of the second, before the second year's deadlines accumulate.
Leaving the SAT to the second year means competing directly with the extended essay and mocks, and then with the exams themselves.
The mathematics section
IB students, particularly those taking Math AA, generally find SAT mathematics comfortable. The content is below their level; what is new is the pace and the multiple choice format.
A small amount of format practice usually closes that gap.
The verbal section
This is where the work is, and it does not come free from IB study. IB English develops analysis and extended writing; the SAT reading and writing section tests something narrower and faster.
Students who assume the verbal section will take care of itself are the ones who end up sitting the exam twice.
What actually goes wrong
Rarely the difficulty. Almost always the collision: an SAT date landing in the same fortnight as two deadlines, decided months earlier by nobody in particular.
Writing both calendars on one page at the start of the year prevents most of it.