This study examined the role of reading disability (RD) risk and environmental protective factors in reading fluency in grade 4. The sample consisted of 538 Finnish-speaking students. Kindergarten measures included the students' risk for RD based on poor achievement in phonological awareness and letter knowledge as well as information on the three control variables: nonverbal ability, level of parental education, and gender. Measures in grades 1-3 included environmental protective factors: classmate reports of peer acceptance; teacher reports of positive affect for the student; and mother, father, and teacher reports of partnership between the home and the school. The students were also tested on their reading fluency in grade 4. The results showed, first, that environmental protective factors, namely, high levels of peer acceptance and positive teacher affect, uniquely predicted students' improved reading fluency in grade 4, after controlling for RD risk, nonverbal ability, level of parental education, and gender. Second, when controlling for the effects of single environmental protective factors, a higher overall number of environmental protective factors predicted students' improved reading fluency in grade 4. Third, RD risk predicted lower peer acceptance, less positive teacher affect, and lower parent-teacher partnership in grades 1-3. Finally, the effect of RD risk on subsequent reading fluency was partially mediated through the overall number of protective factors in the student's interpersonal environment.