Patsy M. Lightbown & Nina Spada 
How Languages are Learned 4th edition – Oxford Handbooks for Language Teachers [EPUB ebook] 

Teachers are often told that new teaching methods and materials are ‘based on the latest research’. But what does this mean in practice? This book introduces you to some of the language acquisition research that will help you not just to evaluate existing materials, but also to adapt and use them in a way that fits what we currently understand about how languages are learned.