Semantic diversity quantifies the similarity in the content of contexts a word has been experienced in. Four experiments investigated its effect on lexical and semantic judgments in 9- to 10-year-olds and adults. In Experiment 1, a cross-modal semantic judgment task, participants decided whether a visually presented word matched an audio definition. Both groups were slower to respond to words high in semantic diversity, and this effect was modulated by task demands. Experiment 2 used the same items but in a lexical-decision task. Children were faster to respond to words high in diversity but there was no effect in adults, failing to replicate previous work. Experiment 3 examined possible reasons for this, and Experiment 4 tested the effect of semantic diversity on lexical decision via secondary analysis of 2 large megastudies. Overall, the facilitative effect of semantic diversity on lexical decision was robust. Our findings show that contextual experience influences subsequent lexical processing, consistent with context inducing semantic representations that reflect continuities and gradations in meaning. These gradations are captured by semantic diversity, and in turn, this interacts with task demands to influence behavioral performance.