This paper examines the implementation of an alternate block (A/B) schedule in three high schools in Irving, Texas. The purpose is to review how time was used in 48 randomly selected high school Algebra 1, Biology 1, English 2, and U.S. History classes. Of the 48 classes, 12 observations were conducted for each course. The findings revealed a predominance of teacher-centered instruction across all courses. Teachers spent the majority of time presenting content and monitoring student seatwork, while students primarily listened to the teacher, responded to teacher questions, and completed seatwork. The most used teacher and student materials (overhead, chalkboard, textbooks, worksheets, notebook paper) further pointed to a teacher-centered environment. Results of checklists revealed a moderately high level of student engagement, little or no individualization of instruction, and a mixed use of thinking indicators. When teacher and student time allocations were compared to expert estimates, large discrepancies were found which further accentuated the lack of student-centered instruction included in the lessons. After 4 years, most teachers had not adapted instruction to take advantage of the longer blocks of time. Implications indicate that teachers needed clear, measurable goals related to instructional strategies and the best use of 90-minute blocks of time. (Author)