Cal Poly San Luis Obispo is the most selective of the California State University schools. Cal Poly admits around a third of all applicants. In the graph above, the blue and green dots represent accepted students. As the data shows, the majority of students who got into Cal Poly had at least a B+ average, an SAT score (CR+M+W) above 1700, and an ACT composite score of 24 or higher. Chances of admission improve as those numbers go up. Realize that in the middle of the graph there's a lot of red hidden behind all that green and blue. Some students who have grades and scores that are on target for Cal Poly still get rejected. On the flip side, some students with scores below the norm got accepted.
Except for EOP students, the California State University system does not ask students for essays or interviews, so the difference between an acceptance and a rejection usually comes down to factors such as your test scores, grades, college preparation, chosen major, and geographic location. Cal State schools often need to give preference to area applicants, and some majors are more restricted than others because of staffing and budget constraints. On the academic front, the more challenging your high school record, the better.
To learn more about Cal Poly, high school GPAs, SAT scores and ACT scores, these articles can help: