This paper examines the independent effects of principal background, training and experience as well as teacher academic qualifications on school proficiency growth through time. The study is one of the first to examine statistically different proficiency growth trajectories using an entire state-wide data set over a long-term, six-year timeframe. The results indicate that there are two statistically significantly different latent school proficiency trajectory for both Chicago and non-Chicago schools. The models suggest that teacher academic qualifications, principal training, principal experience as a principal and an assistant principal, and experience of the principal as a teacher previously in their schools are significantly related to school proficiency growth over time, dependent upon school context. The authors also demonstrate that principal training and background may have an effect on school-level proficiency score growth.