The authors developed a collaborative learning environment (CLE) as a student-centered approach to assist students' understanding of difficult scientific concepts. Computer-facilitated investigative group projects were designed to enhance students' communication and reasoning skills, peer-learning, and peer-teaching. Projects were structured around cost-efficient Web-delivered tasks incorporating re-usable interactive Web components that store student responses in a server database (OCCA, or Online Courseware Component Architecture). These provide for group discussion, self-assessment, and peer review. Student submissions were accumulated in a portfolio to enable them to reflect on their learning. "Facilitutors" contribute to timely feedback using efficient templates for reviewing and annotating student work. Students work in groups (3 per computer) for 4 to 6 hours on their project within scheduled weekly CLE classes of 40 students with one facilitutor (repeated 8 times). Successful attributes of these tasks are described and evaluated, including strengths of on-campus collaborative learning and appropriate training of "facilitutors." (Author/AEF)