Reviews in many countries have found little evidence of consistent advantages in either single-sex education or coeducation. Over the last three decades, coeducation has been introduced into many single-sex schools, but there is a dearth of evidence from the student perspective of the impact of such changes on the classroom learning environment. The Individualised Classroom Environment Questionnaire (ICEQ) was administered to 309 elementary and secondary boys from a single-sex school over 3 years prior to (T1), during (T2) and after (T3) the introduction of coeducation. Overall, boys perceived coeducational classrooms to be significantly more Personalised at T2, particularly at the secondary level, while Personalisation increased significantly from T2 to T3 at the elementary level. No significant changes were evident for the Participation, Independence, Investigation and Differentiation scales at either T2 or T3. These findings have implications for the ongoing single-sex/coeducation debate.