This quantitative study describes how teachers responded to the large-scale, top-down, mandated curriculum and examination reform of the Advanced Placement (AP) program in chemistry. This study analyzed data from a nationwide sample of teachers (N = 1,062) teaching redesigned AP Chemistry courses in the first two years of the curriculum reform. Repeated measures analysis of covariance (RM-ANCOVA) indicated that teachers' perceived challenges about the AP redesign substantially decreased once they gained more experience teaching redesigned AP Chemistry courses. Teachers reported that inquiry laboratory investigations and changes in the AP examinations were the most challenging aspect of the curriculum reform, whereas the use of new textbooks and chemistry content was perceived as the least challenging. With respect to classroom practices, teachers more frequently enacted instructional elements directly related to the AP examination instead of incorporating references to core elements of the curriculum reform in their instruction. Similarly, though teachers reported frequently conducting laboratory investigations in their classrooms, only about 25% of the laboratory investigations included elements of student-generated inquiry, an important component of the redesigned AP Chemistry program. Surprisingly, teachers' self-reported classroom instruction remained similar in both the first year and the second year of the AP redesign. In general, this study suggests that school leaders and administrators should not be discouraged when teachers experience challenges during early phases of curriculum reforms. Adaptation to reform takes time. However, teachers may need special encouragement to adopt more in-depth aspects of curriculum reforms.