Visit your local library and research the materials they have on the topic of language acquisition theories. Ask the librarian for a recommendation if you aren't sure which books are best. Take a look at the professional education journals as they often have articles on the subject.
Call or visit your local community college or university and ask if they have any classes on the theories of language development. Colleges will sometimes offer a course if there is enough interest, so ask if they will start a waiting list for language development theory if there is nothing offered.
Research online sites. Type words and phrases such as "language learning theories," "Skinner and language learning," "Vygotsky's theory of language" and "Chomsky language" into the search engine. Bookmark the sites you want to return to.
Start a language theory notebook. As your read about the different theories, take notes about how they are similar and where they differ. Use a mind map to illustrate the way the theories are represented.