Our understanding about the developmental similarities and differences between oral and silent reading and their relations to reading proficiency (word reading and reading comprehension) in beginning readers is limited. To fill this gap, we investigated 368 first graders' oral and silent reading using eye-tracking technology at the beginning and end of the school year. Oral reading took a longer time (greater rereading times and refixations) than silent reading, but showed greater development (greater reduction in rereading times and fixations) from the beginning to the end of the year. The relation of eye-movement behaviors to reading proficiency was such that, for example, less rereading time was positively related to reading proficiency, and the relation was stronger in oral reading than in silent reading. Moreover, the nature of relations between eye movements and reading skill varied as a function of the child's reading proficiency such that the relations were weaker for poor readers, particularly at the beginning of the year. The relations between eye movements and reading proficiency stabilized in the spring for children whose reading skill was 0.30 quantile and above, but weaker relations remained for readers below 0.30 quantile. These findings suggest the importance of examining eye-movement behaviors in both oral and silent reading modes and their developmental relations to reading proficiency.