We report on a meta-analysis designed to test the theory that instruction that involves direct teaching of academic vocabulary and teaching strategies to determine the meaning of unknown words develops students' abilities to infer new words' meanings and builds students' overall vocabulary knowledge. We meta-analyzed 39 experimental and quasi-experimental intervention studies conducted in grades K-5 to examine the effects of these instructional approaches. Results indicate that interventions that targeted word meaning instruction do not show overall positive effects on measures of breadth of vocabulary knowledge. Although strategy interventions are effective in improving word solving skills on near transfer measures, strategy interventions do not significantly impact students' overall breadth of vocabulary knowledge. These findings suggest that direct teaching of vocabulary words may not be effective for building overall vocabulary knowledge among elementary-grade students. More research is needed to examine the potential of teaching strategies to determine the meaning of unknown words.