Block periods of 75, 90, 100 minutes, or longer require good teachers to continue to develop and improve their teaching skills while keeping the student engaged over a long period. The fewer class meetings in the semester or year, and the rich potential for creativity and innovation provided by the longer period all combine to offer a challenge and an opportunity to high school teachers. This book describes how 11 high school teachers in public high schools in the Seattle area chose to take advantage of this opportunity and respond to this challenge, through self-directed professional development. Each of these teachers, some working alone and some collaborating with colleagues, chose to use the tools of action research to learn more about the effectiveness of their own teaching in block periods and to improve their own teaching--and in some cases, the teaching of their colleagues, as well. The first 2 action-research studies focus on the transition that students make from a middle school, with short periods, to a four-year high school with 100-minute block periods. Further action-research studies explore a variety of issues focusing on instructional planning for the block period and innovative and complex uses of time with the longer period. One action-research study explores structural innovations in a high school program coupled with 100-minute block periods. The final action-research study describes an innovative model for improving teaching and learning in secondary school block periods through the activities of an instructional coach. Appendixes list work sites and responsibilities, measurement tools, and active-learning strategies for math classes. (DFR)