This 1-week study explored the extent to which high school students (n=140) acquired meaningful understanding of selected biological topics (meiosis and the Punnett square method) and the relationship between these topics. This study: (1) examined "mental modeling" as a technique for measuring students' meaningful understanding of the topics; (2) measured students' predisposed; generalized tendency to learn meaningfully; (3) determined the extent to which students' meaningful learning orientation predicted understanding beyond that predicted by aptitude and achievement motivation; (4) examined the consistency of the level of meaningful understanding acquired across the different biology topics; (5) experimentally tested two auto-tutorial instructional treatments (relationships presented to students, relationships generated by students); and (6) explored the influence of meaningful learning orientation, prior knowledge, instructional treatment, and all interactions of these variables in predicting meaningful understanding. The results of correlations and multiple regressions indicated that meaningful learning orientation generally contributed to students' attainment of meaningful understanding independent of aptitude and achievement motivation. Students attained similar levels of meaningful understanding across the different topics and on the relations between the topics. (Author/PR)