One of the long standing complaints of ELL teachers is the lack of quality learning materials. This problem is acute in middle and high School students when they have wider topics to catch up with. Many ELL experts state that the instruction materials available are too simple and disoriented from students’ grade level. The advent of Common Core State Standards has brought some notable changes in English Language Learners education standards. But the challenge is still not fully overcome and teachers have to research different strategies and techniques to improve the education standard.
Here is an interesting article from Education Week about this topic: http://www.edweek.org/ew/articles/2016/05/11/quality-learning-materials-are-scarce-for-english-language.html