Raven Progressive Matrices (RPMs) and Wechsler Intelligence Scale for Children (WSIC-R) are two common general intelligence measuring scales used in Iranian high schools. In this paper the relationships between g factor scales and students’ reading comprehension, grammar, and vocabulary was examined by correlation and regression analysis. Standard tests of grammar and vocabulary and Cambridge Key English Test (KET) were used to elicit the overall language proficiency of Iranian high school students. The results of the study revealed that verbal intelligence and vocabulary and non-verbal intelligence measured by RPMs not WSIC-R were determining factors in reading comprehension. Verbal intelligence was found to have an important role in vocabulary knowledge. Only grammar, in spite of a weak correlation with reading and a section of WSIC-R, didn’t show any remarkable correlation with intelligence or language knowledge measuring scales.
