A blended learning model was developed to enhance lecture delivery in a large, diverse introductory psychology unit, introducing the use of an online, personalized learning system for lecture preparation and using lecture time to extend students' understanding. Changes to the assessment included diagnostic, formative and summative online quizzes. Using hierarchical multiple regression to account for the variance associated with prior achievement and background knowledge, the results show that students who completed the online formative assessments had significantly higher scores on summative assessment tasks, and that scores were even higher for students who used these resources repeatedly. Changes to future implementations of the model are suggested to improve student engagement in formative assessment, and to facilitate lecturer's use of reports on student progress to focus and improve the quality of discussion in the face-to-face lectures. (Contains 6 tables and 3 figures.)