There has been extensive research in the last 20 years on the effectiveness of different instructional interventions and learning conditions on the acquisition of vocabulary. However, very few attempts have been made to explore how vocabulary knowledge develops over time. This paper argues for the need to conduct more longitudinal studies on vocabulary learning and teaching and provides suggestions for important replication studies in the area. In particular, this paper calls for the replication of the studies by Schmitt (1998) and Webb & Chang (2012). Unlike most studies on vocabulary learning and teaching, these two follow a longitudinal approach and study vocabulary growth from two main perspectives, i.e. the development of vocabulary depth and vocabulary breadth. The approximate replications suggested here would constitute an important contribution to the field of vocabulary learning and teaching.