This study investigated the differential effects of two modes of instructional program (conceptual change oriented and traditionally designed) and gender difference on students' understanding of heat and temperature concepts, and their attitudes toward science as a school subject. The subjects of this study consisted of 72 seventh grade students from two General Science Classes taking the course from the same teacher. Each teaching method was randomly assigned to one class. The experimental group received reinforcement via the conceptual change texts while the control group utilized traditionally designed science texts over a period of four weeks. Analysis of covariance was used. Logical thinking ability was taken as a covariate. The results showed that the conceptual change oriented instruction produced significantly greater achievement in understanding of heat and temperature concepts. The result for science attitudes as a school subject showed no significant difference between the experimental and control groups. Also, no significant difference was found between the performance of females and that of males in terms of learning heat and temperature concepts and attitudes toward science, but the interaction of treatment regarding to gender was significant for learning the concepts. In addition, it was found that students' logical thinking ability accounted for a significant portion of variation in heat and temperature concepts achievement. The following are appended: (1) A list of common student alternative conceptions probed by HTCT; (2) A conceptual question example from HTCT; and (3) Excerpt from heat and temperature conceptual change text Temperature and heat. (Contains 1 table.)