Learner-centered instruction is very important concept in virtual and face-to-face classes for enhancing academic performance of students. This research aims to study the status of learner-centered instructions followed by the teachers in online classes during the pandemic and its effectiveness on the mathematics achievement of the learners. The cross-sectional survey design was used by taking 2273 students by convenient sampling from basic to university level of Nepal. The t-test, ANOVA, correlation, and regression techniques were used to analyze the data. The finding of the study indicates that the learning-centered role of teachers was found to be high in mathematics teaching during the pandemic situation in Nepal however teachers are not habituated to give extra time in learning difficulties whereas the problem solving and creative role of teachers were found better as compared to other. Types of the institutions, teaching level, access to the internet, and having tablet are the determinants for the learner-centered instruction in teaching whereas availability of laptop and computer, types of institutions, and access to the internet have significant roles to determine the mathematics achievement. The findings of this research suggest that practice of learner-centered instruction would be useful and beneficial for the learners in online classes.