The present study aims to investigate if grade 9 English students, being 15-16 years old, attending a Swedish secondary school, use English slang during their English as a second language lessons, and if so, why they do it, and if there are any differences between the two genders in their slang usage. In order to incorporate a didactic perspective, it is also examined how English teachers deal with their students’ slang usage. Three English lessons has been observed, alongside with interviews with three English teachers, in order to conduct the investigation. The results indicate that slang words are common during grade 9 English lessons, and the male students’ usage of slang exceeds their female counterparts’ usage to a great extent. Reasons for these results can be found in the field of gender language which argues that slang usage, and language usage in general, is strongly connected to identity, and to how the two genders are expected to behave. Moreover, the English teachers display a varied opinion about their students’ slang usage, yet accounts for utilizing it when teaching register and linguistic adaptation. This approach is approved by a great amount of research, which states that by incorporating youth-language, in this case slang, students are able to gain a linguistic awareness where they can identify with what is taught, as well as adapt their language depending on situation and context.