An investigation was designed to reveal, describe, and assess the rote-level and meaningful-level understandings students attained as they progressed through the learning of new concepts. This study used an assessment technique used in previous research called "mental modeling" to ascertain the nature (meaningful, rote) of the understandings 163 10th grade students acquired. This research also explored factors that may be related to students' acquisition of conceptually inter-related, meaningful understandings, specifically: (1) aptitude, (2) need for achievement, (3) meaningful learning orientation, and (4) gender. The goal of this research was to attain a better understanding of how students may formulate inter-related, meaningful understandings of science concepts. Analysis of the data from the Differential Aptitude Test and need for achievement questionnaire indicated significant gender differences between males and females. Male students scored higher than female students. Meaningful learning orientation was not significantly different between males and females. (PR)