It’s understandable that ESL teachers would like to include something more than language-skill development in their courses. However, this desire can become a mission which can override the real needs of the students.
Teachers who have a passion about a topic, for example, the environment, social justice, animal rights, racism, and technology, can feel, as one colleague explained, “This topic is very important for all students to know about.” This can lead to a theme for a course in which the focus of each lesson is about that topic as students read, write and talk about it and learn the specialized vocabulary connected to it.
A problem can arise when the theme starts to overshadow skill building. For example,
when working on reading skills, if a reading passage has “important” content but is above the students’ reading levels, the teacher will “orally” explain what they read. Students are evaluated on how much they knew about the content rather than on their language-skills development.
As another example, if the conversation or discussion skill that is supposed to be developed during the course isn’t naturally applicable to the theme, it may not be practiced.
Teachers at the next level might find students with a lot of knowledge about causes of air pollution or the challenges of recycling or discrimination in hiring practices or the potential of AI or social media, but weak language skills.
Fortunately, it doesn’t have to be an either-or situation; in other words, we don’t have to choose between skill development or content.
To explore this more, I put together a four-part YouTube video series.
YouTube videos and downloadable exercises, see 
Common Sense Teaching ESL 