The study investigated the impact of dyslexia on the performance of students in English comprehension in Lagos State Secondary Schools. This study adopted an ex-post facto design approach. The target groups for the study were Lagos State Senior Secondary School students in Nigeria. The samples were drawn from four (4) geo-political areas in Lagos State of Nigeria (Ikorodu, Badagry, Lagos Island and Epe). Multi-stage random sampling technique was used to select five co-educational Public

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... y Schools from each of the four geo–political zones. Where fifty (50) Students were selected from each of the schools making a total number of two hundred and fifty (250) students from each of the zone totaling to one thousand (1000) respondents from the four (4) geo-political areas in Lagos State of Nigeria. Two instruments, Reading Deficiency questionnaire which is a researcher based questionnaire and an achievement test in English Comprehension were used to collect data from the respondents. The instrument has two sections; Section A of the instrument focuses on demographic information of the Students while Section B of the instrument contains items eliciting information from the students on reading deficiency. The achievement test was based on reading comprehension. The validity and reliability of the instrument were determined by trial testing the instrument on the similar set of the sample in some other schools that were not part of sample population and the Kurder-Richardson 21 formula was used to obtain the inter-item reliability coefficient of 0.85 and 0.80 respectively. The data were subjected to Descriptive statistics, Pearson product moment correlation coefficient and t-test. Data were tested for significance at the 0.05 level. Based on the findings, it was detected that there is a significant relationship between reading deficiency and students' performance. Part of the recommendations made was that teachers should help students develop strategies for building a good reading habit and proper understanding of language system.