The project produced learner-centered classroom instructional materials for a large-enrollment intro astronomy survey course for non-science majors. Lecture-Tutorials are instructional materials intended for use by collaborative student learning groups, and designed to be integrated into existing courses with conventional lectures. The materials offer classroom-ready learner-centered activities that don't require outside equipment or drastic course revision to implement. Each 15-min Lecture-Tutorial poses a sequence of conceptually challenging, Socratic dialogue-driven questions, with graphs and data tables, designed to encourage students to reason critically about difficult astronomy concepts. Materials are based on research into student beliefs and reasoning difficulties, and use proven instructional strategies. They have been field-tested for effectiveness at various institutions, representing a wide range of student populations and instructional settings. In addition to materials development, a second effort of the project focused on assessment of changes in students' conceptual understanding and attitudes toward learning astronomy as a result of lecture and subsequent use of Lecture-Tutorials. Quantitative and qualitative assessments were completed using a precourse, postlecture, and post-Lecture-Tutorial instrument, with focus group interviews. Collectively, evaluation data illustrate that conventional lectures alone helped students make statistically significant--yet unsatisfactory--gains in understanding (with students scoring at only  50% level postlecture). Further, data illustrate that Lecture-Tutorials helped students achieve statistically significant gains beyond those attained after lecture (with students scoring at 70% level post-Lecture-Tutorial). Quantitative evaluation of student attitudes showed no significant gains over the semester, but students reported they considered Lecture-Tutorials one of the most valuable components of the course.