Sources of mathematics self-efficacy (SMS), which foster the development of self-efficacy belief, can develop differently in students with different cognitive characteristics. The objective of this study was to compare SMS of gifted and non-gifted students after controlling for mathematics achievement. Participants of the study consisted of 106 gifted and 118 non-gifted students in high schools. The study was a causal-comparative design. The data was collected through the Sources of Mathematics Self-Efficacy Scale, and students' self-reported previous fall mathematical grades. The results of the study revealed that after controlling for mathematics grades, while SMS of gifted children sharply decreased, SMS in the non-gifted group slightly increased. In addition, only vicarious experience dimensions of SMS were significantly different between gifted and non-gifted children. In conclusion, being gifted or non-gifted has an impact on the vicarious experience dimensions of SMS after controlling for mathematics achievement. Mathematics grade positively affects SMS in the gifted group and negatively affects the non-gifted group. Teachers are suggested to use achievement as a reinforcer for gifted students but not for non-gifted students.