Critical thinking (CT) is a type of convergent thinking explored when students learn mathematics. This study aims to obtain a comprehensive representation of students' mathematical Critical Thinking (CT) abilities, based on the mathematical ability level. Data were obtained from 35 students using CT skills tests and semi-structured in-depth interviews based on the criteria of mathematical ability levels, which was saturated on the 15th interview. The research was qualitatively analyzed using the systematic grounded theory with the help of NVivo 12 plus software, and two coders (kappa = 0.81) to determine the reliability test comprising of 9 categories and 4 themes. The result showed that the higher the mathematical ability level, the more diverse students' thinking patterns in solving problems related to algebraic functions. These findings are expected to help education practitioners in developing students' counseling skills.