'Language Issue or Learning Disability?'
One place to start in determining if an English-language learner has barriers to learning other than a language barrier is to make sure he or she has normal hearing and vision. That's one practical piece of advice that Caroline Linse, a senior lecturer at Queen's University, Belfast, in Northern Ireland, provides in her article, "Language Issue or Learning Disability?," published in the December issue of Essential Teacher. While the magazine makes some articles available for free, this particular article is available only to members of Teachers of English to Speakers of Other Languages, Inc., which publishes Essential Teacher.
Ms. Linse mentions some considerations that educators may not readily think about, such as that some ELLs might have had untreated ear infections because they didn't have access to health care. Also, if a child was screened and found to have vision problems, it's possible that his or her parents couldn't afford to buy glasses. Ms. Linse lists organizations that help people to get them.
She also gives some good advice about how an educator may begin to determine if a student has learning issues, such as by investigating how well the student has learned in his or her home language.
This issue of how to determine whether a student has only a language barrier or whether something else is going on is a great concern to educators right now, but I haven't seen a lot written about it. EverythingESL.net has an article on it. I've written in-depth articles about ELLs with disabilities only twice (here and here).