We investigated the sustained effects of explicit versus implicit instruction on the breadth and depth of children's vocabularies, while taking their general vocabulary and verbal short-term memory into account. Two experimental groups with 12 and 15 kindergarten children respectively learned two sets of 17 words counterbalanced to be taught first explicitly or first implicitly. Their learning gain was compared with that of 21 no-treatment control group children. Both explicit and implicit instruction prompted broader vocabulary knowledge; explicit instruction also prompted more in-depth vocabulary knowledge. These effects sustained over time. Individual variation showed that in implicit instruction, children with low short-term memory seemed to gain more breadth of vocabulary in the short run, but also to forget more in the long run. In explicit instruction, verbal short-term memory and vocabulary tended to facilitate the breadth of vocabulary in the long run.