Resource: How Content Teachers Can Teach Language
All teachers who have English-language learners in their classrooms are "language teachers," regardless of the subject they teach, write the authors of a book released by WestEd aimed to improve education for adolescent English-language learners.
I think what the authors of the book, Scaffolding the Academic Success of Adolescent English Language Learners: A Pedagogy of Promise, mean is that all mainstream teachers SHOULD be language teachers if they have ELLs in their classrooms.
The book spells out an approach to teaching language in regular content classrooms called Quality Teaching for English Learners, or QTEL, which Aida Walqui has developed. It's based on five principles: rigor, high expectations, high-quality teacher and student interactions, a focus on language, and having a high-quality curriculum (see excerpts here). Walqui is the director of the teacher professional development program at WestEd. She has co-written the book with her husband Leo van Lier, who is a linguist and sociocultural theorist.
The book, which sells for $27.95, draws on Walqui's experience in implementing QTEL in schools in New York City, Austin, and San Diego. What always stands out for me in listening to or reading about Walqui's recommendations for ELL instruction, is that ELLs need plenty of opportunity to talk about what they are learning. She's an advocate of helping students to develop strong oral-language skills on the subjects they are studying, something that is getting more attention in the field these days.