This study investigates the impact of individual diversity on English as a Foreign Language (EFL) development among Indonesian university students. Utilizing a cross-sectional method, the study compares the language proficiency of third and fifth-semester students, revealing a low diversity of academic vocabulary across both groups. Subsequent analysis identified three key factors influencing language development: cognitive abilities (aptitude), language interaction (exposure), and learning strategies/motivation (behavior). These findings highlight the need for EFL pedagogy to: 1) Introduce diverse recurrent multi-word sequences (RMS) early on. 2) Encourage students to actively incorporate RMS in their writing. 3) Provide constructive feedback on RMS usage. By acknowledging and addressing individual diversity, EFL pedagogy can better support students in achieving their full language learning potential. Keywords: Language Development, Individual Diversity, Aptitude, Exposure, Behavior.