This paper reports on a study which investigated the effect on vocabulary recall of introducing new words via two different methods. A one-group quasi-experimental research design with alternating time series measures was employed. A group of 60 fourth graders were taught 80 carefully selected words either in semantically related sets or semantically unrelated sets. Also under investigation was the effect of these methods on test completion. The statistical analysis revealed that learning words in semantically unrelated sets yields better results than learning vocabulary in semantically related sets. The difference persisted in the long term. Further, test completion time was much longer for the semantically related vocabulary items, indicating a slower recall of vocabulary. The study indicated that, contrary to frequent practice in many course books, presenting new vocabulary that belongs to the same semantic set together may cause interference due to cross-association and may even hinder vocabulary learning. Such practice needs to be questioned and alternative methods that involve presenting vocabulary in unrelated sets need to be developed to facilitate vocabulary teaching and learning. (C) 2008 Elsevier Ltd. All rights reserved.