Tierra, a Spanish-speaking child, attended a school in which some of her classmates were native Spanish speakers and some were native English speakers. Instruction and class work were done evenly in both languages. This instructional approach is

C) two-way immersion

Explanation:

Important feature of the situation given above is that some students are Spanish and some English native speakers. Unlike the situations where majority of students is native in one language, and where the best approach would be one-way immersion, here, the best instructional approach would be two-way immersion. In this approach, two groups of students serve as both, the language model for their native language, and learners of the other language.