The transition to high school is the most critical time to determine on-time graduation.

The number of unexcused absences quadruple from 8th to 9th grade. (Allensworth, 2013)
Students across the 8th grade achievement spectrum experience significant grade declines in all subject areas when they transition to high school. (Rosenkranz, T., de la Torre, M., Stevens, W.D., & Allensworth, E.M. (2014). Free to fail or on-track to college: Why grades drop when students enter high school and what adults can do about it. Chicago, IL: University of Chicago Consortium on Chicago School Research) Nationwide, 9th graders are three to five times more likely to fail a class than students in any other grade. (Southern Regional Educational Board, 2002)
Nationwide, 9th graders are three to five times more likely to fail a class than students in any other grade. (Southern Regional Educational Board, 2002)

Who will graduate can be accurately predicted based on course grades in 9th grade.

Students who are on-track at the end of their 9^th grade year—earn at least a quarter of the credits needed for four-year graduation and receive no more than one “F” in a core course—are as much as four times more likely to graduate from high school than their off-track peers. In fact, the 9^th grade on track metric is more predictive of a student’s likelihood of graduating than race, ethnicity, poverty level and prior test scores combined. (Allensworth, 2013)
For every full-year course that a 9^th grade students fails, their chance of graduating in four years decreases by 30%. (Nield, 2009)
70-80% of all students who failed 9th grade will not graduate from high school. (Wyner et al. (2007). Achievement Trap: How America is Failing Millions of High-Achieving Students from Lower-Income Families. Jack Kent Cooke Foundation.)

By implementing the “Freshman Success Approach” developed by the University of Chicago Network for College Success, Chicago Public Schools increased 9^th grade on track rates by an astonishing thirty-three percentage points since 1999 and its graduation rates rose by twenty-five percentage points over that same time frame. (University of Chicago, 2018)