Importance: Because of the high prevalence of myopia in Taiwan, understanding the risk factors for its development and progression is important to public health. Background: This study investigated the risk factors for myopia and their influence on the progression of myopia in schoolchildren in Taiwan. Design: Patients’ clinical records were obtained retrospectively from ophthalmologists. Questionnaires were given to collect demographic information, family background, hours spent on daily activities, myopia progression, and treatment methods. Participants: A total of 522 schoolchildren with myopia from a regional medical hospital in northern Taiwan participated the study. Written informed consent was obtained from the participants of legal age or the parents or legal guardians. Methods: Multivariable regression analyses were performed. Myopia measured in dioptres was analysed, controlling for patients’ family and demographic information as well as their daily behaviours. Main Outcome Results: Children with high myopic parents were more myopic. Earlier onset age of myopia was associated with a higher level of myopia and greater annual myopic progression. Children reporting more near work activities had higher levels of myopia and greater progression of myopia. Lower levels of myopia were associated with more exercise, longer periods of sleep, and better vision care knowledge in children and parents. Intake of food supplements had no effect on myopia. Conclusions and Relevance: In addition to genetics, education, environment, and near work activity can influence the development of myopia. Health policies for schoolchildren should promote protective activities and vision care knowledge in order to protect the eyesight of schoolchildren.