Besides teachers knowledge of subject matter, their proficiency in pedagogical content knowledge (PCK) is a strong determinant of what student can and do learn.This study sought to establish teachers' proficiency level in mathematical knowledge for teaching (MKfT) by examining teachers' interpretations of students' problem solving strategies. A sample of Kenyan high school mathematics teachers participated in the study whose central thesis was that, effective learning of mathematics depended on teachers' level of proficiency in PCK. Study instruments included questionnaires, classroom observation portfolio and interview schedules. Findings which were categorized as Fluent, Standard and Mediocre showed that teachers levels of proficiency in PCK were multidimensional across the components of PCK.These mixed proficiency levels explain the observed inconsistent and weak evaluative acts by the teachers at classroom level resulting into low achievement in mathematics by secondary school students. The study recommends a cyclic model that addresses the dynamic nature of mathematics education and support teachers to progress systematically towards expertise in MKfT a component of PCK .