The purpose of this study was to develop a screening test for children at risk of reading underachievement and to investigate the effectiveness of the early-stage intervention program. In the first part of the study, we recruited 155 elementary first grade students for a screening test. Phonological deletion, digit naming, object naming, and sound-letter correspondence knowledge of a screening test, all assessed at the beginning of the school year, predicted the reading ability at the end of the school year. In the second part of the study, we analyzed the difference in the reading ability between fourteen children who participated in the intervention program and eighteen non-participating children. Reading ability was assessed by evaluating word recognition, oral reading fluency, reading comprehension, and pseudo-word recognition. The reading ability of intervention group improved more compared to control group, and the difference between two groups accentuated over time. However, final analysis conducted in November revealed that two groups did not differ significantly in oral reading fluency. This suggests that, unlike word recognition and comprehension, fluency might not dramatically improve in a short period.