Despite reports suggesting numerous academic and social behavior deficits in boys with fragile X syndrome (FXS), little information is available concerning their actual classroom academic and social behavior. In this study, direct observational data were collected on the behavior of 26 elementary school-age boys with FXS during classroom academic activities in primarily self-contained special education classrooms. Results indicated moderate levels of academic engagement during periods of academic instruction, comparable to that of their classroom peers. Classroom engagement was not related to intrasubject variables such as severity of delay, autism status, or medication usage. A general measure of classroom quality and instruction was significantly correlated with engagement. Relatively low levels of stereotypic or self-injurious behavior were observed. These findings are discussed in relation to the existing engagement literature for school-age individuals with disabilities and issues concerning syndrome specific behaviors.