The aim of this study was twofold: firstly, to investigate the grade level (elementary and middle school) and gender effect on students' motivation in science (perceived academic science self-concept and task value) and perceived family involvement, and secondly to examine the relationship among family environment variables (fathers' educational level, mothers' educational level, and perceived family involvement), motivation, gender and science achievement in elementary and middle schools. Multivariate Analysis of Variance (MANOVA) showed that elementary school students have more positive science self-concept and task value beliefs compared to middle school students. Moreover, elementary school students appeared to perceive more family involvement in their schooling. Path analyses also suggested that family involvement was directly linked to elementary school students' task value and achievement. Also, in elementary school level, significant relationships were found among father educational level, science self-concept, task value and science achievement. On the other hand, in middle school level, family involvement, father educational level, and mother educational level were positively related to students' task value which is directly linked to students' science achievement. Moreover, mother educational level contributed to science achievement through its effect on self-concept.