Correct Response: C. Research in second-language acquisition suggests that a language-learning environment is most effective when students are presented with comprehensible content, or input. Furthermore, to ensure ongoing language growth, the level of linguistic input should be just above the students' current language proficiency level but scaffolded in such a way as to be understood. In SEI classrooms, comprehensible content/input is a critical element of instruction. Effective SEI teachers seek to integrate new and unknown words, phrases, and concepts with familiar ones in order to make the input challenging yet accessible to English learners. A is incorrect because second-language instruction using an SEI approach is focused on promoting English learners' development of academic language proficiency for academic achievement, not on developing students' social language skills for interpersonal communication. B is incorrect because learners are grouped according to their level of English language proficiency in Massachusetts SEI programs, not by their native-language backgrounds. D is incorrect because virtually all instruction and materials in SEI programs are in English. Students do not receive 40 percent of their instruction in the first language.