While it is widely accepted that language teachers require knowledge of second language acquisition (SLA) (Richards, 2010), what about content teachers, who are increasingly required to help develop their learners' academic language proficiency? How much do they need to know about SLA theories and how can they acquire such knowledge and expertise? This article proposes P. Nation's (2007) "four strands framework" as a straightforward and accessible model for content and language integrated learning (CLIL) teachers to address the challenge of balancing content and language instruction, a common concern within CLIL programs. The article begins by looking at two well-known CLIL teacher competence frameworks. It then raises questions about the extent to which CLIL teachers need to master aspects of pedagogical content knowledge about SLA. The authors argue that while CLIL teachers do indeed need knowledge of how languages are learned and of SLA-informed approaches to developing learners' second language (L2) proficiency, questions about just how much SLA knowledge CLIL teachers need and how they can be equipped with this knowledge remain unanswered. By delineating language learning opportunities into the four strands framework--meaning-focused input, meaning-focused output, language-focused learning, and fluency development--the authors illustrate how this framework offers a practical guide for integrating language and content education effectively in CLIL and bilingual education contexts. The article ends with a presentation of three principles to help CLIL teachers achieve both the content and language teaching objectives of CLIL.