This study attempts to verify the efficacy of a learning-oriented diagnostic assessment (LODA) system, which provides individualized feedback based on automated process-oriented error analysis for teaching communicative English grammar to tertiary level EFL learners. The LODA program is designed to provide three types of corrective feedback presented in a process-oriented manner: elicitation, metalinguistic feedback, and explicit correction. This study compares the control group of 28 and the experimental group of 21, who participated in the LODA program that was administered for five weeks to college students enrolled in an EFL grammar course. It was found that the LODA program strongly facilitated the acquisition of communicative English grammar through the two types of process-oriented corrective feedback, the elicitation exerting more positive effects than the metalinguistic feedback. A comparative analysis of the frequency and percentage of linguistic and cognitive errors revealed that sentential structures and omission errors had the slowest rate of uptake. The results suggest that the computerized LODA system has great potential for providing EFL learners with individualized diagnostic feedback. Finally, the survey results suggest that most of the respondents thought favorably of the LODA system equipped with individualized diagnostic feedback.