Prior research has shown that people can use the co-occurrence statistics of words and referents in ambiguous situations to learn word meanings during a brief training period. The present studies investigate the effects of allowing some words and referents to appear more often than others, as is true in real learning environments. More frequent word-referent pairs are oftenbut not alwayslearned better, and also boost learning of other pairs. Superior learning for training sets with varying pair frequency may be a result of learning frequent pairs first, and using this knowledge to reduce ambiguity in later trials to learn other items. However, contextual diversity the number of other pairs a given pair appears with is naturally confounded with frequency, and presents an alternative explanation. The experiments in the present study systematically manipulate three critical factors in cross-situational learning frequency, contextual diversity, and within-trial ambiguity and measure their individual and combined effects on statistical word learning.