Large-group circle time is an important component of many preschool classrooms' daily schedules. This study scrutinized the teaching content of Head Start teachers' literacy instruction (i.e., the types of literacy concept embedded within the instruction, lexical characteristics of teachers' talk, and elaborations on literacy knowledge) in two different large-group activity contexts (book reading and nonbook reading) that occur during large-group circle time at the beginning and the end of fall semester. Change in teachers' literacy instruction across the semester and within each context was examined. Results indicated that teachers engaged in more literacy instruction in the nonbook reading context than during book reading. Teachers provided more vocabulary instruction than code-related instruction during book reading, but a similar amount of each type of instruction during nonbook reading. More vocabulary instruction occurred in winter than in fall, whereas the lexical characteristics of teachers' talk and elaborations of newly introduced literacy knowledge remained stable. This study provides an approach to distinguishing different components of teachers' literacy instructions. The findings point to the potential of efforts to strengthen teachers' evidence-based literacy instruction during non-book-reading group activities. (author abstract)