That less than 40% of candidates who took the Senior School Certificate Examinations in Nigeria between 2009 and 2015 had credits and above in English language and Mathematics has become a source of worry to all stakeholders. Results of research efforts to provide plausible explanations to the problem have been inconclusive. Also, not much had been done to assess the contribution of teachers' knowledge indices as likely sources. This study therefore investigated the predictive value of Teachers' Depth of Subject Content Knowledge and Depth of Pedagogical Knowledge on Students' Academic Achievement in English Language and Mathematics. Specifically, the study investigated which category of teachers (B.Ed. /B.Sc.Ed. /B.A.Ed.; PGDE; or B.A. /B.Sc) had the deepest Depth of Subject Content Knowledge; the deepest Depth of Pedagogical Knowledge; the deepest Depth of Subject Content and Professional Knowledge; and the predictive ability of Depth of Subject Content and Professional Knowledge for Students' Academic Achievement. The sample comprised seventy-eight English Language and Mathematics teachers from thirty-two randomly selected secondary schools in Kwara State; and the intact SS II classes taught by the teachers. Quantitative data were collected through tests, observations and vignettes; and analysed using descriptive and inferential statistics. Findings showed that teachers with B.Sc. demonstrated the deepest Depth of Subject Content Knowledge, Depth of Pedagogical Knowledge and Depth of Subject Content and Professional Knowledge. Also, pedagogical and subject content knowledge of teachers were found to be significant predictors of Students' Academic Achievement. Significant differences were observed between the Depth of Subject Content Knowledge and Depth of Pedagogical Knowledge of the English Language and Mathematics teachers in favor of Mathematics teachers. Similarly, students' performance in English Language was lower than that of Mathematics, though not statistically significant. These findings raised concerns of profound implications for teacher education curriculum in Nigeria.