This study aimed to investigate the effectiveness of a learning management plan designed using the GPAS 5 Step model in enhancing the learning achievement of 31 Thai language learners in the area of sentence structure. Participants were selected through cluster sampling from a population of Thai language learners in a public school. The research instruments included the learning management plan, a learning achievement test, and a questionnaire to assess participant satisfaction with the learning experience. Data were collected using a one-group pretest-posttest design. Descriptive statistics, paired samples t-test, and an effectiveness index with a criterion of 80/80 were employed for data analysis. The results indicated that the learning management plan designed using the GPAS 5 Step model had a significant positive impact on participants' learning achievement in sentence structure. Additionally, participants reported high levels of satisfaction with the learning experience, highlighting the effectiveness of the GPAS 5 Step model in creating an engaging and satisfying learning environment. These findings contribute to the growing body of research supporting the effectiveness of the GPAS 5 Step model and emphasize the importance of participant satisfaction in language learning contexts.