Having a weak vocabulary can negatively affect part of your SAT essay score. For the new SAT essay, you are scored in three different areas:
- Reading: How well you show you've understood the essay prompt (the passage you're writing about and analyzing in the essay)
- Analysis: How well you manage to dissect the author's argument and explain why the author's argumentative techniques are persuasive and how they persuade the reader
- Writing: How well you are able to convey your points, using appropriate language.
If you have a weak vocabulary, it will most likely affect your Writing score. As our analysis of the SAT essay rubric explains, part of writing a strong SAT is using a wide variety of appropriate vocabulary. This doesn't mean throwing in random big words like "indeterminable" or "perspicacious" into your essay out of context, but rather using precise and formal language. For instance, rather than writing about "the things the author does to make the reader believe her," it would be better to write about "the techniques the author uses to persuade the reader."
Since part of the Writing score is also dependent on varied sentence structure and ability to clearly convey ideas, it is possible to receive a decent (4-6 out of 8) Writing score without using high level vocabulary if you are still organized and focused; however, in order to get a top SAT essay score, you're going to need to use at least some advanced vocabulary effectively.