Assigned reading materials in Swedish universities are often in English. Therefore, pupils planning to pursue higher education need to develop a good receptive knowledge of English academic vocabulary. However, previous research indicates that upper secondary pupils completing obligatory English instruction may lack sufficient knowledge of English academic vocabulary. This study further explores Swedish pupils’ knowledge of receptive English academic vocabulary, focusing on how it is influenced by word frequency and word class types, two factors found to impact L2 learner vocabulary knowledge. Moreover, we examine correlations between vocabulary test scores on word frequency and word class types and self-reported extramural English activities. Ninety-three pupils at a Swedish upper secondary school completed a vocabulary test and a questionnaire about their extramural English activities. The results showed that pupils performed significantly better on high-frequency words than low-frequency words. An analysis of how high- and low-scoring pupils answered different questions revealed some different tendencies in their receptive English academic vocabulary knowledge. We also found that low scorers performed more poorly on verbs than nouns and adjectives. Moreover, engagement in extramural English activities, such as reading and social media, was positively correlated with the vocabulary test scores, most consistently with scores on verbs. Based on the findings we discuss the need for pedagogical strategies for effective teaching of English academic vocabulary, including well-planned integration of extramural English activities into the English classroom. Such pedagogic support could help Swedish upper secondary pupils develop English academic vocabulary needed for success in higher education.