Two groups of English as a second language students engaged in a fourteen-week repeated reading (RR) treatment: (1) a 3x group (n = 16), which engaged in three readings per session, and (2) a 5x group (n = 15), which engaged in five readings per session. Reading rate and background knowledge were measured at five points to assess the effect of treatment length as well. Results from a mixed effects repeated measures ANCOVA model showed that neither treatment group nor treatment length had a significant effect on reading rate, but background knowledge did. The model also revealed that the fixed effects (e.g., treatment, duration, and background knowledge) explained 8.1% of the variation in reading rates (R[superscript 2] = 0.081). The random effects of individual variation and text variation explained 0.9% (R[superscript 2] = 0.009) and 0.3% (R[superscript 2] = 0.003) of variance in reading rate respectively, meaning the entire model could explain 9.3% of the variation (R[superscript 2] = 0.093). It was concluded that reading three times per session was more efficient than reading five times per session, and background knowledge is a variable that must be controlled for in reading studies.