This study aimed to develop an automated computer scoring system (ACSS) incorporating a Korean spell checker to assess students' constructed responses and to check the efficacy of this system. To accomplish this, we examined the performance of automatic spelling correction in reporting and correcting spelling errors, the interaction of gender and grade level in making spelling errors, the relationship between spelling errors and academic achievement, and the scoring efficacy of an ACSS that incorporated a spell checker. The analysis of percentage, two-way ANOVA, t-test, Pearson's correlation, and human-computer correspondence were conducted. The results revealed that an automatic spelling correction system could report 66.44% and correct 26.78% of all total misspelled words. We also found gender and grade-level differences in misspelling words. Students misspelled fewer words as they advanced in grade level, and male students misspelled more words than females. In terms of the relationship between spelling errors and concepts, we found that the number of concepts included in student's responses had a significant relationship with the total number of written words and misspelled words. This indicates that students who made more spelling errors had discussed more concepts in their responses. Based on these results, we discuss practical implications for preventing students' responses being scored lower due to spelling errors caused by being less attentive using an ACSS with a spelling correction system.