Under the bilingual education system in Singapore, Chinese Singaporean students are required to be proficient in both Chinese and English languages. The education environment in Singapore is dominated by English, which in turn affects the development of reading ability in Chinese among students. To understand the development of Chinese and English reading abilities of Singapore children, we conduct research which include testing, questionnaire and interview of seven-, nine- and twelve-year-old Singaporean students, their parents and teachers. The students take the Chinese and English PIRLS and PIRLS-Literacy reading comprehension tests first, and then the PIRLS questionnaires. The univariate analysis of variance and the linear regression are used to comparatively analyze and discuss the data of tests and questionnaires by age and family language background (FLB), and to investigate the relationship between English and Chinese reading abilities. Secondly, we conduct semi-structured interviews with the parents and teachers selected by critical student cases according to their testing and questionnaire data, in order to discuss their growth of reading ability. We then categorize the data and analyze using social network analysis (SNA). Finally, we conduct structured observations on the two cases with maximum variation 2 sampling in order to find out the challenges involved. The study discovers that English language interferes significantly in the early stages of Chinese vocabulary accumulation, but such kind of interference decreases with age. Nine years old is the critical age when such interference decreases significantly. The results also show that the key factor affecting reading ability is vocabulary accumulation.