This quantitative study focuses on the relationship between foreign language learners' aptitude and proficiency test scores. Four groups of 136 beginning students received six months of Initial Acquisition Training (IAT) in four different language categories, according to the level of complexity for an English speaker: French (Category I), Indonesian (Category II), Tagalog (Category III), and Arabic (Category IV). This study attempts to identify variations within the correlation among those four languages by analyzing the relationships between aptitude and proficiency scores from each category. The data gathered consisted of students' Defense Language Aptitude Battery (DLAB) and Oral Proficiency Interview (OPI) test scores. Results showed that the correlation between DLAB and OPI was moderate amongst French and Tagalog languages, the correlation with respect to Indonesian was almost nonexistent, and null for Arabic. The complexity of the foreign language categorization process, tests' reliability issues, and a fixed course length regardless of language category are some factors that could have contributed to the calculation of different correlation coefficients. Further studies based on experimental research are recommended to help substantiate causality to the findings derived from this study.