Microcomputer-based laboratory (MBL) tools and guided discovery curricula have been developed as an aid to all students, including the underprepared and underserved, in learning physical concepts. To guide this development, extensive work has been done to find useful measures of students' conceptual understanding that can be used in widely varying contexts. This paper focuses primarily on the evaluation of student conceptual understanding of mechanics (kinematics and dynamics) with an emphasis on Newton's 1st and 2nd laws in introductory courses in the university. Student understanding of mechanics is looked at before and after traditional instruction. It is examined before and after MBL curricula that are consciously designed to promote active and collaborative learning by students. The results show that the majority of students have difficulty learning essential physical concepts in the best of our traditional courses where students read textbooks, solve textbook problems, listen to well-prepared lectures, and do traditional laboratory activities. Students can, however, learn these fundamental concepts using MBL curricula and Interactive Lecture Demonstrations which have been based on extensive classroom research. Substantial evidence is given that student answers to the short answer questions in the Tools for Scientific Thinking Force and Motion Conceptual Evaluation provide a useful statistical means of evaluating students' beliefs and understandings about mechanics. Evidence for the hierarchical learning of velocity, acceleration, and force concepts is presented.