@Ski_Mom
What are the subscores (math-reading)?
They do not need more content to do better in SAT math. What they might need is perhaps a different approach in solving the problems. More maturity and practice will help. They just have to see the SAT as what it is and try to get themselves in to the “mind” of the test, the patterns and types of questions etc. One might perfectly know all content and still get tripped by SAT questions by making silly mistakes, misreading questions etc. I would suggest pay more attention to the format of the test and highlighting areas of weaknesses. For example when a problem is given at a school test always what you do is solving it and then presenting solutions. However SAT at times will ask for a variation of the solution and a student that had solved the problem 100% correctly might not pay attention and present to wrong part of the solution.
The Reading can also be improved by maturity and reading more complex text. Are they taking any AP English/history classes? Those can help because the students are regularly exposed to original sources and do lots and lots of reading.
SAT is not just a knowledge test. Maturity and targeted practice can help.
Also to put some perspective 1430 is still a good score.