There are two SAT Subject Tests for Mathematics: SAT Subject Test Mathematics Level 1 and SAT Subject Test Mathematics Level 2. A full description and practice questions can be found on the Collegeboard site here.
SAT Subject Test Mathematics Level 1 is a little more demanding and slightly more difficult than the mathematics required for the SAT and ACT mathematics and therefore should not require very much additional preparation.
SAT Subject Test Mathematics Level 2, however, is a markedly more difficult examination, which requires a more profound understanding of additional areas of mathematics at a more generally elevated level. There is a lot of time pressure in the examination: 50 questions in 60 minutes. Very few, even of the very best, manage to complete all 50 questions, though it is still possible to attain an 800 score by leaving up to 8 blanks (assuming, of course, that all the other questions have been answered correctly). Therefore, it is not only important to know all the material/syllabus inside out but it is equally important to be very quick and efficient at answering the questions.
It should be noted that the more highly ranked universities will not consider SAT Subject Test Mathematics Level 1 as an entry requirement, insisting on prospective students to take SAT Subject Test Mathematics Level 2. And for certain degrees, such as Engineering, SAT Subject Test Mathematics Level 2 is a prerequisite.
At AGF Tutoring we have tutors who have scored perfect scores in the SAT Subject Test Mathematics and thus know very what preparation and which test-taking strategies are required to score an 800. If you are interested in preparing for either SAT Subject Test Mathematics Level 1 and/or 2 then please register here or book your free introductory session.