Here are three ways that the SAT Essay differs from what the ACT calls its Writing section.
1. Timing: The SAT allows 50 minutes to complete the essay section, while the ACT allows 40 minutes. The SAT requires that students read and understand a relatively lengthy passage before they begin to write. If you read rapidly with strong comprehension, the SAT essay may be a good option.
2. Analytic depth: The SAT requires you to analyze how an experienced writer accomplished his or her goals (and also grades clear reasoning and use of language). The ACT Writing section requires that you build a persuasive essay around a central thesis. You must reference introductory statements but are free to build on your own ideas.
3. Complexity: Both essays require strong analytical skills. The SAT Essay provides rich source material. The ACT Writing is a more free-form test, allowing plenty of freedom to craft your response. If you excel at analyzing others’ work, read quickly and accurately, and appreciate having a framework for your own writing, the SAT essay may be a good choice. If you can create a thesis from a simple prompt, are quick to organize your thoughts, and aren't the strongest at analytical reading, you may score better on the ACT essay.