This study aims to verify the effects of narrative therapy-based Self-Regulation Strategy Development (SRSD-NT) training on the writing competence, self-esteem, and subjective well-being of writing-underachieved children. A total of 18 students (9 males and 9 females) in grades 5 and 6 at D Elementary School were selected as participants through a series of screening tests. Six children each were assigned to the experimental, comparison, and control groups through randomization, and the children in the experimental and comparison groups were given 10 sessions of training for 80 minutes once a week. The treatment was SRSD-NT training for the experimental group, standard SRSD training for the comparison group, and no treatment for the control group. To verify the effectiveness of the training, pre-post and delayed tests were conducted and repeated measures analysis of variance was performed. Results SRSD-NT training had a positive and sustained effect on improving writing-underachieved children’s writing skills, self-esteem, and subjective well-being. This study shows that SRSD-NT training is as effective as standard SRSD training in improving writing-underachieved children’s writing skills and is more effective than standard SRSD training in improving writing-underachieved children’s self-esteem and subjective well-being.