This paper reports on part of the first phase of a longitudinal project investigating the development of academic language in English as the Language of Teaching and Learning (LoLT) by Foundation phase learners in two different educational contexts. In the first context, the learners were all English additional language (EAL) learners taught by EAL teachers. In the second context EAL and English first language (L1) learners were taught by L1 teachers in integrated classes. The three groups of Grade 1 learners were assessed on the semantic subtests of the Diagnostic Evaluation of Language Variation Criterion, Referenced Edition, which evaluate the psycholinguistic processing skills underlying lexical acquisition and organization. Vocabulary learning is central to the development of academic language and literacy. There were statistically significant differences between the three groups on all measures. The EAL learners in the first context had significantly lower scores than the EAL and L1 learners in the second context, and the EAL learners in the second context had significantly lower scores than their L1 peers. Pre-school exposure to English and gender did not have significant effects, except on the subtest assessing fast mapping of novel verbs. The results provide information on what can reasonably be expected from EAL learners in Grade 1, suggest language skills that can be addressed to support the learners, and have implications for language in education practices with EAL learners in different educational contexts.