The aim of this study is to determine whether 5th grade students' reading comprehension changes according to their chronotype when effects of their gender are controlled for 384 5th grade students (age range 11-12) from elementary schools in Sakarya participated voluntarily in the research. An achievement test to determine the level of reading comprehension of students, and the morningness-eveningness scale for children to specify their chronotype, were used. The achievement test was given twice - at 9: 00 am the first time and again, one month later, at 1: 15 pm. Covariance analysis (ANCOVA) was applied to assess if there were differences between performance at the comprehension task that depended upon chronotype (morning-, neither- or evening-types). A significant statistical difference was found in reading comprehension between the first and second times of testing when effects of gender were controlled. In neither test there was a significant effect of chronotype upon reading comprehension. When measurements of the two tests were compared, reading comprehension decreased on the second occasion in morning-types, while it increased in neither-and evening-types. We conclude that timing the reading lessons in accord with students' chronotype will increase their reading comprehension.