What’s the hardest part of the SAT?

That completely depends on your current strengths and weaknesses. Some find the math portion much harder than the writing or reading portions, and vice versa. The hardest part to improve upon is probably the Critical Reading section, only because it involves more deeply ingrained, long-term bad habits that need to be broken before you can excel. But no portion of the test is “hard” or “easy,” objectively. Any student can achieve incredible SAT scores. As with any test: effort in = results achieved!