The skill-development model contends that achievements have an effect on academic self-confidences, while the self-enhancement model contends that self-confidences have an effect on achievements. Differential psychological processes underlying the 2 models across the domains of mathematics and science were posited and examined with structural equation modeling using the data of grade 8 students from the Trends in International Mathematics and Science Study across 28 countries (N = 144,069), which generated 2 major findings. In statistical terms, (1) there were "negative" cross-domain paths leading from achievements to self-confidences, controlling for the positive matching domain paths, as predicted by the skill-development model across domains; (2) there were "positive" cross-domain paths leading from self-confidences to achievements, controlling for the positive matching domain paths, as predicted by the self-enhancement model across domains. There were, however, qualitative variations in the degrees of support for the 2 models across countries.