To make the assignment slightly more involved, have students design and justify a direct replication, a systematic replication, a conceptual replication, and an extension of the original study.
To help students, review the concepts of internal validity, external validity, construct validity, and power. Then, discuss the difficulties of getting any of these validities, much less all of these validities in one study. Remind students that enhancing one of these factors may be at the expense of another factor (table 4.3 can be used as a jumping off point for discussing tradeoffs involved in making design decisions.).
Therefore, revising a study may simply involve making different tradeoffs than the original author did.