CD-ROM developed by Maarten Dolk and Catherine Twomey FosnotFacilitator’s Guide developed by Antonia Cameron, Sherrin B. Hersch, and Catherine Twomey FosnotIn their Young Mathematicians at Work series, Catherine Twomey Fosnot and Maarten Dolk described Mathematics in the City, an innovative project where teachers helped young children construct a deep understanding of number and operations in a math workshop environment. Now they and two colleagues from the project have developed a 21st-century approach that provides pre- and inservice teachers with an interactive, video-based, digital context for inquiry into the teaching and learning of mathematics.Designed for workshop leaders and college instructors, the Addition and Subtraction Minilessons Resource Package consists of three valuable components: A CD-ROM that offers users a multi-media learning environment for professional development on topics ranging from instruction to assessment, and that stimulates action, reflection, and discussion with dynamic video clips, children’s work samples, and interviews with students and teachersA Professional Development Overview Manual that provides general advice on teaching in a digital environment A Facilitator’s Guide specific to the CD-ROM that includes suggestions for using the video clips; sample dialogue from field-tested sites; facilitation tips; and more.In Addition and Subtraction Minilessons, clips of real teachers conducting effective minilessons in real classrooms show you how these short, focused sessions can build big mathematical thinking in young learners.Users also are able to study teachers at work: designing rich contexts for problem solving; listeningto, questioning, and interpreting students’ thinking; drawing connections between mathematical ideas and strategies; and, ultimately, developing a vibrant mathematical community.