Prompting learners to generate examples has been proposed as an effective way of developing understanding of a new concept. However, empirical support for this approach is lacking. This article presents two empirical studies on the use of example-generation tasks in an online course in introductory university mathematics. The first study compares the effectiveness of a task prompting learners to generate examples of increasing and decreasing sequences, with a task inviting them to classify given examples; it also investigates the effectiveness of different sequences of generation and classification tasks. The second study replicates the investigation of interactions between generation and classification tasks. The findings suggest that there is little difference between the two types of task, in terms of students' ability to answer later questions about the concept.