Iranian High School Students Performance on Reading Comprehension of Their English Course book: Analyzing the Effects of Unknown Vocabulary

The main purpose of this study was examining the percentage of vocabulary size or vocabulary knowledge required for comprehending high school English coursebook texts in grade three. To reach this aim, the students performance on texts with different levels of unknown vocabulary densities was examined. Another purpose of the study was to determine the threshold level of comprehending English texts of high school coursebook in grade three. Through determining this level, it would be possible to see what percentage coverage was set that above which comprehension would be adequate and below which comprehension would be inadequate. To conduct the study and reach the aims of the study, 50 students were randomly divided into five homogeneous groups. The subjects in each group answered to a reading comprehension test containing texts with different densities of unknown vocabularies (an intact text, and texts with 1% to 5% unknown vocabularies). At the end, the students were scored based on their performance on the reading comprehension tests. The ANOVA statistical analysis was used to determine the differences in the group performances on the tests. Results revealed that the students who took the intact texts performed better than those who took the tests with manipulated texts. ANOVA analysis confirmed such differences (F = 86.371, sig. = .00, p<0.01). A stepwise regression analysis demonstrated that there was not a threshold level set for the high school students which determines above and beyond the comprehension of texts

Keywords:

Reading comprehension , Unknown vocabulary , EFL , Threshold level , Iranian high school students , Vocabulary size