Ninth grade is a critical juncture for students--and can be a jarring transition. Even students a strong track record in the middle grades can experience academic difficulty, and those who enter high school with poor course grades, weak attendance, or behavior problems are especially at risk. An early misstep can have lasting implications: students who fall off track at the beginning of the school year may find it difficult to recover, and ninth graders who fail to earn the required number of academic credits are at elevated risk of dropping out. To support their most vulnerable students, high schools first need to identify them. This report uses eighth-grade student record data from two cohorts of first-time ninth graders (2015-16 and 2016-17) in the School District of Philadelphia (SDP) to examine which student characteristics are most predictive of falling off track in ninth grade. With this information, schools can use middle grades data to identify their most at-risk ninth graders--and intervene to help them start strong in high school.