Foundational skills are often viewed as necessary components for automaticity in reading and writing. In this study, we draw on teacher interviews to explore what secondary English/language arts teachers identify as necessary language for successful school writing. Findings suggest that teachers believe White mainstream English is a necessary component for academic success, although interviewees could not recall ever being explicitly taught this idea. Furthermore, teachers experience a tension between wanting to engage in culturally and linguistically responsive pedagogy and their (often unexamined) underlying beliefs about White mainstream English being part of foundational language. We discuss how teachers' understanding of language skills includes their beliefs about what is deemed "correct" and "appropriate" for school and discuss the hidden ways foundational skills reinforce White mainstream English-centric ways of knowing. We offer recommendations for teachers to examine their own biases in foundational language for writing.