This study, investigated Predictive Validity of Students’ Achievement Scores in Basic Education Certificate Examination (BECE) on Achievement in Senior School Certificate Examination (SSCE) conducted by NECO in Mathematics. Three research questions and three null hypotheses guided the study. The sample of the study comprised 3910 candidates sampled from 7 randomly drawn unity schools within Ebonyi and Abia states of Nigeria for the period under study (2014 – 2019). The official BECE scores and SSCE scores in mathematics of the students domiciled in NECO headquarters Minna, Niger state, Nigeria served as data for the study. Data collected were analyzed using Pearson’s Product Moment Correlation to answer the research questions and Multiple Regression statistics to test the hypotheses at 0.05 level of significance. The analysis of the data revealed that BECE scores have a strong validity with the students’ achievement in SSCE mathematics examination. Furthermore, there was a statistically significant relationship between the students BECE scores and their achievement in SSCE mathematics examination. Based on the findings of the study, it was recommended among others that the BECE preparation of the students should be given serious attention because of its proven predictive value on achievement at the SSCE level. Keywords: Mathematics, Predictive Validity, and Academic Achievement DOI: 10.7176/JEP/12-21-03 Publication date: July 31 st 2021