Although school boards and colleges try their best to group students of similar language abilities together, students all come from different backgrounds. Some countries place high value on English learning, and students from these countries may have had significant language training already. The more fundamentals a student has been taught, the faster he can progress in the next stage of learning. The more English he already knows, the better he can comprehend lessons in English. If a student possesses functional knowledge of English, he can use it outside of the classroom to read books, newspapers and signs, watch television, and listen to the radio and music. The effects of this immersion will spill over into his class work. A student with little or no previous training in the language, however, will depend entirely on his ESL teacher for language acquisition.
Some linguists theorize that babies have the potential to master phenomes, that is, sounds or accents, of any language. As they age and learn their native language, however, pronouncing foreign phenomes, not to mention internalizing foreign grammatical systems, becomes increasingly difficult. Adults find this the most difficult of all. Therefore, the age of a student affects her language acquisition. Adult students prove much slower language learners than children.
A student's natural propensity for language in general affects his ability to acquire a new language. A Korean student who was never very good at Korean grammar will find English grammar, which introduces a host of new grammatical concepts, even more challenging. This impediment to learning English is difficult for ESL teachers to detect, as they can not observe students operating in their native language (unless the teacher also happens to speak that language).
Some parents of ESL students make the decision for their children to study in the U.S. and because the students cannot see any personal benefit of learning English, they find little motivation to try. Other students who have goals of getting accepted into U.S. colleges or achieving a competitive TOEFL score will work hard in class and devote their free time to studying. This kind of motivation will speed up their language acquisition.