Hello,

Scholastic Assessment Test ( SAT ) is an entrance exam used by most colleges and universities in the US, Canada as well as other countries to select students for admissions to undergraduate courses. However, it is just one factor in the admissions decision. Schools also consider your high school GPA, academic transcript, letters of recommendation (LoR), interviews and personal essays.

The best time to take SAT depends on a variety of factors: the schools to which you're applying, your application deadlines, your cash flow and your personality.

The SAT is a standardized test that measures a student’s skills in three core areas: Critical Reading, Math, and Writing. Students in classes 11 and 12 take SAT so that they can submit their scores to colleges as part of the college application process.

I would say you should register atleast at the start of 12th standard and keep a check on the dates as there is major difference between semester timings of the year.

Ihope this helped

All the best