This study assessed knowledge of numerically quantified English sentences in two learner populations--second language (L2) learners and deaf learners--whose acquisition of English occurs under conditions of restricted access to the target language input. Under the experimental test conditions, interlanguage parallels were predicted to arise from acquisitional pressures imposed by derivational economy on universal grammar (UG)-guided semantic interpretation. The results of a task in which participants matched sentences to multiple discourse depictions confirmed the predicted parallels. However, in matching underinformative sentences to depicted contexts, the L2 and deaf learner groups overactivated discourse-pragmatic knowledge. The restriction of indefinite noun phrases to singleton indefinites and the cancellation of scalar implicatures rendered sentences more informative in underinformative contexts, producing incorrect--although principled--interpretations. These results inform English acquisition at the interface of semantics and discourse pragmatics and provide further support that economy pressures yield L2 learner and deaf learner interlanguage parallels as observed, for instance, in learners' interpretative knowledge of universally quantified English sentences.