Luke - not sure which aust state u r in and each is a bit different. In general though the maths standard requirement is relatively low and any maths contributing to your AtAR is probably fine (Algebra 1 is pretty basic maths).
For NCAA academic eligibility u need to satisfy 4 things: graduate High School; satisfy the SAT/ACT test requirements; satisfy GPA requirement and satisfy core-course requirements.
Contrary to the post above, NCAA does not look at ATAR or consider any admission to any Aust university as supporting their eligibility requirements. The SAT test has nothing to do with ATAR.
For NCAA D2 you need a SAT score of 820+. This test is held globally 6 times per year, u need to register with the college board and book early - places fill. Aim to sit it at least twice.
Your NCAA GPA is calculated on your core course results in subjects done for your leaving certificate (varies for each state eg in Vic the unit 3&4 core-course grades on the statement of results).
U also need to have 16 core-courses in years 9-12 with the specified mix of courses for D2. U need to check these as some students have not been eligible because they did not do the specified range of subjects (English, Maths, Science, Social Science, Languages etc). U can do 1 extra after graduating High School but much better to do them at High School.
NAIA require u satisfy 2 of the following 3 criteria: SAT of 860+, GPA of 2.0+, ranked in the top 50% of your year 12 class.
If r considering NAIA then u need to register separately with their eligibility center.
As well as satisfying the NCAA/NAIA academic eligibility requirements, u also need to satisfy the university admission requirements which may be higher or lower depending on the university u r seeking to attend.
Hope this helps.