The purpose of this study was to conduct content, criterion-related and construct validity on the Physical activity and Snacking Efficacy Scale for Children (PASE-C). Convergent validity was obtained by correlational analysis of the PASE-C subscales with instruments that measure the same constructs as the PASE-C subscales. This study was part of a larger ongoing investigation of the effects of a mentoring program on eating behavior, physical activity and self-efficacy in overweight upper-elementary students. The nonequivalent control group pretest-posttest design was used in the larger study in which participants in the treatment group underwent a 10-week mentoring intervention while students in the control group did not receive this intervention. The PASE-C is an 18-item instrument designed to assess personal goal setting and decision making efficacy for physical activity and health food choices. Respondents answered on a 5-point Likert scale ranging from 1 = 'Not sure at all' to 5 = 'Completely sure'. Face validity was established using an expert panel in self-efficacy appraisals. The questionnaire was piloted with 4th and 5th grade children including cognitive interview testing of the questionnaire. The items on the PASE-C were developed based on the current related literature, interviews with children and evaluation of the pilot study results. The items represent the impediments or challenges children may experience when attempting to improve physical activity and eating behaviors. The multidimensional scaling analysis suggests that the PASE-C is three-dimensional. However, the most clear and interpretable dimension in both pretest and posttest data analyses was the self-efficacy dimension. This dimension differentiated between items assessing self-efficacy to be physically active and self-efficacy to make healthy food choices. This finding supported the construct validity of the PASE-C. Evidence from the Pearson’s correlations between PASE-C subscales and the BSEQ and CDSE also supported the construct validity of the PASE-C. The PASE-C physical activity efficacy scores had a strong, positive correlation with the BSEQ, a measure also designed to measure a child’s physical activity self-efficacy. The PASE-C snacking efficacy subscale scores also correlated highly with the CDSE, a measure designed to assess a child’s self-efficacy to make healthy food choices. The PASE-C subscales also appeared to be largely unrelated to measures assessing different constructs as evidence by small, non-significant correlations between the PASE-C subscale scores and the SPAN physical activity behavior and nutrition knowledge subscales. These findings contributed further evidence supporting the construct validity of the PASE-C scores.