Purpose – The purpose of this paper is to examine the independent effects of principal background, training and experience as well as teacher academic qualifications on school proficiency growth through time. Design/methodology/approach – The authors analyzed the entire population of all elementary and middle schools in the state of Illinois, n=3,154 schools, from 2000 to 2001 through 2005-2006 using growth mixture modeling. The authors examined growth at the school level in the percentage of students meeting or exceeding standards on the Illinois Standard Achievement Test, analyzing separate models for Chicago and non-Chicago schools. Findings – The results suggest that there are two statistically significantly different latent school proficiency trajectory subgroups through the six-year time period, one high and one low, for both Chicago and non-Chicago schools. In addition, 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. Practical implications – Recent studies on the independent effects of principal experience, training and teacher academic qualifications have shown inconsistent results on school achievement growth. The authors demonstrate that principal training and background may have an effect on school-level proficiency score growth. Originality/value – This 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. [ABSTRACT FROM AUTHOR]