This study piloted a reading comprehension instruction professional development intervention for teachers of upper elementary grade students (Unlocking Understanding), exploring the relative effects of two versions of the intervention that varied the degree of lesson scripting. Results indicated a statistically significant difference between the fully scripted and partially scripted (i.e., increasingly teacher-planned) groups on one of three student outcome measures. Specifically, students in classrooms with partially scripted lessons performed better on a statewide reading test (ES = 0.42) than did students in classrooms where teachers used fully scripted lessons. However, there were no significant group differences on two other reading comprehension measures. Teachers reported a high degree of satisfaction with the training, although they stated a preference for fully scripted lessons compared with partially scripted ones. Teachers in both conditions were able to deliver the lessons with acceptable fidelity. Implications for professional development are discussed.