The dramatic increase in time for amusements that young people in the USA enjoy suggests that the use of time in school is more important than ever. Carroll (1963) pointed educational researchers to the importance of classroom time nearly fifty years ago. Carroll’s model (see Figure 1) is a quasi-mathematical one in which three of the five classes of variables that explain variance in school achievement are expressed in terms of time. In a 25-year retrospective consideration of his model, Carroll (1989) stated that ‘the model could still be used to solve current problems in education’ (p. 26). I concur and recommend that educational designers and researchers reconsider his model and its emphasis on time as a critical variable in educational effectiveness (Anderson, 1985). Research and development initiatives that hope to be relevant must take time and its use by teachers and learners very seriously.