The current investigation made an attempt to study the contributory effect of language proficiency,
discipline-related knowledge, and content specificity on Iranian EAP students' performances on
neighboring and non-neighboring reading comprehension tests. To this end, 160 graduates and
undergraduate students of biology and psychology, both male and female holding BA, MA, and PhD
degrees were selected through snowball sampling from different universities of Iran including
Maragheh, Semnan, Babolshahr, Urmia, Saveh, Tabriz, Tehran, Zanjan to participate in the quantitative
study. All the participants were administered five online tests including Vocabulary Level Test (VLT),
two Farsi knowledge tests, and two content cloze tests. A mixed factorial ANOVA was used to analyze
the collected data. The results indicated that the contributory effect of English proficiency on
Iranian ESAP students’ reading comprehension is significantly fluctuated with changes in
content specificity of ESAP reading tests. Furthermore, it was concluded that content specificity
may be something beyond text difficulty which measured by quantitative indices. Therefore, there is an
open question of what content specificity is. The findings of the present study have implications for test
developers and researchers in the field ESAP assessment.