This study investigated spelling errors in English stories written by 206 students in an elementary school implementing Korean/English immersion education. Errors were analyzed using crosstab and MANCOVA. Findings are as follows. Spelling errors occurred in 4 categories in order from the most frequent to the least: substitution, omission, addition, and transposition. The error occurrences differed depending on grade level changes: lower grades (Grades 1-3) vs. higher grades (Grades 4-6). The students in both grade levels made more errors in substitution and omission: these error types were significantly decreased as they progressed to the higher grade levels. Errors in addition and transposition showed much fewer occurrences for both grade levels, and these errors did not show a significant decrease because of their rarer occurrences. Overall, the students’ spelling ability increased remarkably as they progressed in grade levels in the immersion environment.