English CLIL-instruction in Sweden is supposed to be beneficial to students who want to improve their academic English vocabulary proficiency in preparation for studies or employment abroad. However, recent research shows that there is no difference in academic English proficiency between students in upper secondary school CLIL-programs and students in regular upper secondary schools in Sweden. Furthermore, educational researchers question if CLIL-programs in Sweden qualify to be defined as CLIL-instruction since Swedish translanguaging is extensively used which does not make the programs 100% Englishmedium instruction. Through teacher observations and questionnaires, this study investigates the classroom practices at a CLIL-program in Sweden in addition to ask the CLIL-teachers about their teaching strategies in regards to promoting students’ acquisition, development, and use of academic English. The findings include that the classroom practices are in accordance with practices considered beneficial to students’ proficiency in academi c English by numerous previous studies. In addition, all the teachers questioned in this study purposely work to support and develop students’ academic language proficiency in their respective subject areas and across the curriculum. The study also found four possible factors that perhaps can undermine the acquisition, development and use of academic English vocabulary and those include the following: First, the teachers believe that the students are already sufficiently fluent in academic English, and thus concentrate more on content than on language in their instruction. Secondly, extensive translanguaging in the classroom is common in addition to the students’ habit of speaking Swedish to each other in stude nt-tostudent communication. Thirdly, the students do not receive the corresponding level of education in their native language of Swedish as they do in English, which can have detrimental effects on their abilities to develop their English past their Swedish language abilities. Finally, classroom practices that are not inclusive of all students can work to undermine the acquisition and use of academic English vocabulary.