This study examined the effectiveness of a researcher-provided intervention with 4th-graders with significant reading difficulties. The intervention emphasized multi-syllable word reading, fluent reading of high frequency words and phrases, vocabulary, and comprehension. To identify the participants, 1,695 fourth grade students were screened using the Gates MacGinitie Reading Test, and those whose standard score was 85 or lower were included in the study (N=485). Participants were randomly assigned (2:1) to receive either researcher-provided intervention (n=324) or intervention provided by school personnel (business as usual, BAU) (n=161). Findings revealed no statistically significant differences between students in the researcher-provided intervention and BAU groups. Using effect sizes as an indicator of impact, students in the researcher implemented treatment generally outperformed students in the school implemented treatment (BAU). Examining growth in standard scores, both groups made significant gains in reading outcomes with standard score growth from pretest to posttest of 3 standard score points on decoding, 5 on fluency,, and 2.0 to 7 standard score points on reading comprehension measures.