This study focused on the ability of ESL students to revise their grammatical errors and produce more accurate writing in the future based on error codes. As the researcher, I analyzed the writing over time of four different students who received error codes. I examined three error types for three of the subjects, and two errors types for the fourth subject. The error types included verb errors, preposition errors, determiner errors and plural/singular confusion errors. I analyzed these errors to determine the correction ability and accuracy on future writing of the students.;The subjects were 4 males, two from Malaysia, one from Korea, and one from Japan, enrolled in an academic English course at Iowa State University in the fall of 2006. All the students wrote four essays each throughout the semester, with three of them being examined for this study. This amounted to a total of 12 essays that I examined, three for each subject. The procedure for determining the students' ability to accurately revise their grammatical errors based on codes involved error counts, corrections, and accuracy percentages. To determine accuracy on future writing for the specific errors, a tally was kept of the total number of errors for a specific type on Papers 1, 2, and 4, along with the number of correct uses and accuracy percentages of the errors. I examined the frequency in the chosen error types throughout one semester to determine the ability of the students to produce more accurate writing.;The results show that the students were successful in terms of correcting their errors based on codes and, in general, they were able to produce more accurate writing in the future for the specific error types examined. While not every student showed improvement in accuracy for every error type, the majority of the students were able to improve their accuracy for the targeted errors on subsequent assignments.