English learner (EL) students face the challenge of learning a new language while simultaneously learning other subjects. Similarly, English as Second Language (ESL) teachers have the added responsibility of teaching academic language in STEM subjects to EL students, in addition to language teaching. This article explores how a participant researcher as an ESL teacher collaborated with two mainstream teachers and a science teacher, to enhance EL's language and STEM literacy. Four teachers participated in the study, with one science graduate and one participant researcher, an ESL graduate student, working in a public middle school to co-design and co-teach science lessons. The study analyzed the effectiveness of their semester-long collaboration on the learning of domestic and EL students using mixed methods, such as observations and surveys. The results indicate that ESL teachers and students benefit from the support of pre-service teachers for both STEM content and language. This suggests that placing STEM major graduate students in ESL classrooms and ESL major graduate students in STEM classrooms for their practicum can re-connect language to content literacy development for EL students.