The role of language proficiency in EAP test performance is a hotly contested issue in the field, and, more specifically, disciplinary distance is assumed to mediate such a relationship. The purpose of this study was twofold: a) to investigate the role of English proficiency in teacher-constructed ESAP tests serving achievement purposes; and b) to examine whether with variations in disciplinary distance the role of language proficiency would fluctuate. To this aim, 110 English majors were given TOEFL followed by four ESAP tests: law and psychology as neighbor and chemistry and geology as non-neighbor disciplinary fields. Data analyses revealed that there were statistically significant differences across proficiency levels, and the participants took advantage of their proficiency stock more, and statistically so, when sitting for disciplinarily close rather than distant ESAP tests. Also, the positive effect of disciplinary adjacency was not bound to any linguistic thresholds. Except for geology, moderate to large positive correlations were found between proficiency and ESAP test scores. Findings and implications are discussed vis-à-vis studies addressing the role of language proficiency in EAP assessment in general and ESAP assessment in Iran in particular.
