The purpose of this research is to discuss the longitudinal changes of the out-of-school literacy practices of South Korean elementary students from third to fifth grades and to examine the dependent variables to estimate growth over three years. This research analyzed the data of 909 individual students over three years (2013, 2014, 2015) by the Latent Growth Curve Modeling. The dependent variables are individual student (gender, literacy attitudes, time for media use, perceived difficulties of literacy practices, time for school tasks), family (family members’ literacy practices, conversations with family members about literacy practices) and environment (numbers of books at the school library, frequency of library use). The results are as follows: First, the amount of literacy practices decreased over three years from Grades 3 to 5. Second, all the variables except perceived difficulties and time for school tasks were found to predict the initial status, while literacy attitudes, perceived difficulties and teacher factor were found to predict the growth rate. The results have the following implications on the out-of-school literacy practices of elementary students and literacy education in schools. First, the students whose initial literacy attitudes were high, were found to have a steep decrease in their amount of out-of-school literacy practices. Therefore, students with positive literacy attitudes also need educational support in order to keep their attitudes positive. Second, students’ perceived difficulties of literacy practices were found to be a statistically significant variable to predict the growth rate. Therefore, it is important to reduce students’ learning quantity in order to enhance their interest and time for literacy practices. Third, the amount of students’ media use is found to have no statistical significance in terms of predicting the growth rate. Therefore, follow-up research is needed in order to investigate the opportunities and risks of media literacy practices regarded as new literacy practices in the media environment. Fourth, students’ voluntary out-of-school literacy practices need more educational attention and support.