Two studies examined response to varying amounts of time in reading intervention for two cohorts of first-grade students demonstrating low levels of reading after previous intervention. Students were assigned to one of three groups that received (a) a single dose of intervention, (b) a double dose of intervention, or (c) no intervention. Examination of individual student response to intervention indicated that more students in the treatment groups demonstrated accelerated learning over time than students in the comparison condition. Students' responses to the single-dose and double-dose interventions were similar over time. Students in all conditions demonstrated particular difficulties with gains in reading fluency. Implications for future research and practice within response to intervention models are provided. (Contains 10 tables and 8 figures.)