The environmental conditions experienced in UK schools not only influence the effectiveness of teaching and learning but also affect energy consumption and occupant behaviour plays a critical role in determining such conditions. The aim of this study is to understand occupant behaviour in controlling window blinds in UK primary schools which not only mediate internal conditions but also influence the use of artificial lighting and consequently electricity consumption. Occupant behaviour in controlling blinds against direct solar gain and glare through windows in 140 classrooms of 22 primary schools between 2007 and 2008 was studied through questionnaires, interviews and observations of blind status. Results show that on average blinds are closed very regularly in all the schools except one. This is due to a wish to prevent overheating, reduce glare and also limit the impact of distractions from outside, as some classrooms are located on the ground floor. Such behaviour affects both the effectiveness of teaching and learning and also electricity consumption and consequently a school’s carbon foot print. It is also likely to be at least in part responsible for the gap between design the energy consumption predicted at the design stage and that actually experienced when the school is in use. Designers need to understand the implications of this behaviour to ensure they deliver effective, energy efficient spaces that perform as anticipated.