Career and further education aspirations, educational progress and perceptions of the learning environment were measured annually over three years in primary and secondary boys from a single sex non-government school, following the changeover to coeducation. Hierarchical Linear Modelling analyses revealed the significant role played by the career aspirations of cohorts on boys' progress over time. Further education plans and perceived difficulty of schoolwork were also significant influences, with difficulty at the grade level affecting boys' progress over time. Furthermore, satisfaction with life at school at both cohort and grade levels was a significant determinant of boys' educational progress. These findings suggest new directions for research into single sex/coeducational learning environments. (Contains 2 tables and 2 figures.)