This study aims at measuring the amount of the effect of the reader's background knowledge on performance in reading comprehension tests through the assessment of information gained in reading comprehension (RC) tests across-four testing techniques, short answer questions ,true-false items, multiple-choice items, and cloze test and re-test. This technique involves the examinees in two types of tasks, i.e. pre-reading and post-reading task. Two hypotheses have been proposed to achieve the aims of this study. They are 1-There are no significant differences between the prereading and post-reading performances of examinees on reading comprehension(RC). 2-There are no significant differences in information gain scores across the different techniques of testing reading comprehension (RC) in EFL. To verify the validity of these two hypotheses, a number of statistical procedures have been used such as arithmetical mean, t-test for correlated and independent samples to analyze the performance of third and fourth year College students studying at the Department of English at University of Baghdad/Ibn Rushd College of Education for Humanities on two reading passages taken from TOEFL practice tests (2011). The analysis of the data has shown the following results: 1-The background knowledge has an effect on the performance on reading comprehension (RC). 2-There is a significant difference in students' performance on reading comprehension (RC). 3-The effect of background knowledge is investable on reading comprehension (RC) tests, but it can be identified or neutralized. Based on these conclusions, the researcher presented a number of recommendations.