I am so glad you asked! The SAT may not have a section explicitly labeled “vocabulary,” but you’ll be hard-pressed to succeed on 3/4ths of the test without a vast knowledge of the English language! The four sections of the SAT are: Reading, Writing and Language, Math, and the (optional) Essay. It will be difficult to traverse the Reading section if you don’t know what the words mean, and the “Writing and Language” section actually does have an explicit vocabulary component. Moreover, you can be quite certain that the people scoring your essay are paying close attention to your word choice, as well! Vocabulary is a foundational building block for 3/4ths of the SAT. 

If it were me, I’d talk to my parents about getting a Vocabbett membership around 8th or 9th grade. It’s around this time that your vocabulary will start to naturally stagnate outside the academic environment, so by introducing Vocabbett at this time, you’re able to keep your brain learning the way it learned the majority of your native tongue — through repeated, incidental impressions!