Previous studies on English spelling have investigated the types of spelling errors and their frequencies, and studies on why learners made those errors have been called for. This study aimed to identify factors leading to errors in the English-spelling of Korean elementary school students. The factors were investigated by using the following methods: A total of 130 students from O Elementary School were given three types of word-writing tasks: dictation of single words, dictation of short sentences, and writing words as many as the students can based on pictures depicting familiar scenes. The errors in their writing samples were classified into five types. The students were interviewed about why they made those errors. The results showed that the errors were influenced by the factors: the students’ first language, background knowledge, pronunciation, and morphological reasons. The results suggest that if teachers understood these factors, they would be able to explore better teaching methods for reducing errors in English spelling, and that future research could apply these factors for further investigations.