CPS goes by highest scores on down (30% of seats awarded by rank, 17.5% of seats go to highest scorer from each Tier) until a freshman class is filled. Hence, the computer seats all students who scored 900 points (maximum score) to their first choice schools, then it looks at those who scored 899, 898, 897, etc and sees if that student had the points for their 1st choice school, and if not, it looks to see if that score was enough for the 2nd choice, then 3rd, etc.