This action research project sought to develop students' critical thinking skills by implementing a variety of instructional strategies. Targeted for this study were students in one early childhood special education program, one kindergarten class, and one eighth grade science class. The deficit in critical thinking and problem-solving skills was documented through teacher observation checklists, student journals, and surveys of teachers, parents, and students. Analysis of probable causes revealed that students were not challenged to use critical thinking skills in the classroom on a consistent basis. Several instructional strategies were used in an 11-week intervention to boost students' critical thinking skills, including environmental enhancements, graphic organizers, journaling, problem-based learning, technology, and questioning techniques. Teachers guided students in a variety of developmentally appropriate activities to assist individual, small, and whole groups in problem-solving activities and in acquiring concepts and skills. Pretest and posttest data were collected on the skills of sorting, recalling, describing, problem solving, predicting, and estimating. Post-intervention data revealed definite improvements in student critical thinking skills for most students in the early childhood, kindergarten, and eighth-grade classes. (Thirty appendices include data collection instruments and sample instructional materials. Contains 17 references.) (KB)