As a member of the Ivy League, Brown University is one of the country's most selective colleges. In the graph above, the blue and green represent accepted students. You can see that the great majority of students who got into Brown University have a nearly perfect 4.0 GPA, an ACT composite score above 30, and a combined SAT score (CR+M+W) of above 2100. Hidden beneath the blue and green in the upper right corner of the graph is a lot of red, so even students with a 4.0 and extremely high standardized test scores get rejected from Brown. It's one of the reasons I recommend that all students consider Brown a reach school, even if your scores are on target for admission.
At the same time, don't give up hope if you don't have a 4.0 and a 2400 on the SAT. As the graph shows, a few students were accepted with test scores and grades below the norm. Brown University, like all members of the Ivy League, has holistic admissions, so the admissions officers are evaluating students based on more than numerical data. Students who show some kind of remarkable talent or have a compelling story to tell will often get a close look even if grades and test scores aren't up to the ideal.
To learn more about Brown University, high school GPAs, SAT scores and ACT scores, these articles can help: