Scholars have at various points discussed the needs of second language (L2) writers enrolled in “mainstream” composition courses where they are mixed with native (L1) English speakers. Other researchers have investigated the experiences of L2 writers in mainstream classes and the perceptions of their instructors about their abilities and needs. Little research, however, has directly compared L1 and L2 students (mostly Generation 1.5) taking composition classes together. For this article, the researchers collected writing samples from 56 L1 and 74 L2 students enrolled in a university (mainstream) first‐year composition course. Using a mixed‐methods design, they analyzed the texts for language error counts as well as measures of lexical and syntactic complexity; they juxtaposed these with insights from survey responses of both groups of writers and in‐depth interviews. They conclude that, although L1 and L2 students have much in common, the L2 students had observed and (self‐)perceived language needs that were significantly different from those of the L1 students. These included differences in linguistic accuracy, lexical diversity, and language‐related anxiety. Implications for pedagogy include recommendations for teaching L2 writers to self‐edit for common patterns of errors and sensitize students to the value of nuanced and purposeful lexical variety in their writing.