Assessing the retention of knowledge is the first step of environmental education programs. The low education level in rural areas is one factor influencing habitat loss in Madagascar. We tested whether environmental education lessons given to teachers from a municipality, Iaboakoho, in a priority area for lemur conservation were retained after one year. Questionnaires were given to teachers from Iaboakoho and from other three neighbouring municipalities (control groups). Teachers from Iaboakoho had higher scores than the others. Knowledge gained was retained and might be transferred to children. Increasing proenvironmental attitudes and behaviours is the next step to reduce environmental exploitation.