A lot of research evidence has shown that extensive reading (ER) is very effective in enhancing students’ language proficiency and learning attitude. However, there has been little research on the effectiveness of the ER program with elementary school EFL students in Taiwan in general and elementary school aged underachievers in particular. The purpose of this study was to explore the possibility of using extensive reading as a remedial program to improve the learning performance and attitude of elementary school EFL underachievers in Taiwan. Three fourth-grade English underachievers participated in the program. Thirty half-hour ER sessions were carried out over one semester. The researchers collected data through participant-observation, interviews, review of documents, running records of oral reading, researcher’s journal, a letter identification test, and two high-frequency word recognition tests. The results of this study showed that after the ER program, all three remedial students increased their letter and vocabulary knowledge. Their reading speed and accuracy rate also improved. However, only one of the students was able to perform at an above average level in their regular English class after the program was completed. In addition, the three participants’ learning attitudes changed positively after completion of the ER program. Specifically, participants became more engaged in English learning in school, had more confidence in learning English, and were able to gain satisfaction from reading independently and extensively.