Student knowledge in a subject area prior to and after instruction has traditionally been assessed by administering a pre- and post-test, usually multiple choice, though recent studies criticize the use of even the best-constructed multiple choice tests. This study assessed college freshmen's knowledge before and after a laboratory experience in molecular genetics, based on results from pre- and post-lab clinical interviews and multiple choice tests. The specific areas addressed by this research were: (1) students' misconceptions and missing concepts in molecular genetics as revealed by interviews; (2) changes in student comprehension and knowledge as a result of laboratory instruction as revealed by interviews; (3) student scores on both multiple choice tests and interview tasks; and (4) discrepancies found between knowledge expressed on multiple choice tests versus interviews. Study results indicated that interviews were effective in revealing student misconceptions and missing concepts and that the amount of data generated by interviews was substantially greater than information gained from multiple choice test scores on student comprehension of concepts in molecular genetics. Concept maps are included and appendices contain the test instruments and interview transcripts of representative students. (ML)