The SAT (Scholastic Assessment Test) and the ACT (American College Testing) are two of the most widely recognized college entrance exams in the United States. Determining which exam is harder is subjective and can vary depending on individual strengths and weaknesses. However, based on general trends and data, the ACT is often considered slightly more challenging.

The ACT covers four main sections: English, Mathematics, Reading, and Science. The Science section, in particular, is a unique component that is not present on the SAT. This section requires students to analyze and interpret scientific data, which can be more challenging for some students. Additionally, the ACT includes a Writing section, which is optional on the SAT. The Writing section on the ACT requires students to write an essay in response to a prompt, which can be time-consuming and stressful for some test-takers.

According to a report by the National Center for Education Statistics (NCES), the average ACT composite score in 2021 was 20.8, while the average SAT Evidence-Based Reading and Writing section score was 529 and the Math section score was 526. This suggests that, on average, students tend to perform slightly better on the SAT in Reading and Writing, while the ACT has a slight edge in Mathematics.

Furthermore, the ACT's scoring system is different from the SAT's. The ACT uses a 1-36 scale, while the SAT uses a 200-800 scale for each section. This can make it more difficult for students to understand their performance on the ACT, as the scoring is not as straightforward as on the SAT.

In conclusion, while both exams have their own challenges, the ACT is often considered slightly harder due to its unique Science section, optional Writing section, and different scoring system.