What are the factors affecting literacy development for ELLs?

The rate at which English Language learners develop proficiency in English varies considerably among students, based on a variety of contextual and personal factors. Therefore, teachers will need to know and understand each student individually.
Personal variables influencing literacy development include the age when the language was learned, level of proficiency in the language, parents' proficiency in English, cultural norms for language use, background knowledge, exposure, motivation and attitudes toward the languages. Student's age and the age at which English was introduced are important factors to consider when designing literacy instruction for ELL's. The challenge is that educators are to select materials and activities that are age and level appropriate. Students who did not start learning English at a young age will be developing literacy a lot slower than those who started out young. Learning for older students is a lot more arduous. Another important factor is the literacy level in the native language. As linguists suggest, literacy transfers across languages. Learners who are literate in their native languages are not clean slates when it comes to learning to read and write in English. They are already familiar with the basic principles of reading applicable to most languages such as grapho-phonemic correspondence, word-concept relationship, chunking of the text into sentences, etc.
Student background knowledge and exposure are the factors that will influence the students' ability to construct the meaning, comprehend a variety of texts. Teachers will need to provide extra help to the students, who have had limited exposure, as building background knowledge is essential to meaningful learning.
Home literacy habits, parents' education level, attitudes towards literacy, perception of the function of literacy can also affect the learner's attitude, motivation and proficiency. Families' concept of literacy and their practices can be congruent or may be very different from the school's. For example, respect for the student's own language, even if it is not used for instruction, will favor learning because it reflects respect for the students themselves and their families.
One of the contextual factors that influence literacy development for ELLs is the native language characteristics. For example, Spanish is an efficient language to teach children to read. The writing system is similar enough to English to allow students to master reading within a few years. The situation will be different for Chinese students whose native language has a writing system quite different from English. Therefore, teachers will need to utilize different literacy instruction techniques in order for Hispanic and Asian students to achieve the same educational goals.
Brisk, M. & Harrington, M. (2000).
Literacy and Bilingualism: A Handbook for
All Teachers. Mahwah, NJ: Lawrence Erlbaum Associates.