Secondary students who struggle with reading often have deficits in the area of reading comprehension. The purpose of this study was to examine the effects of explicit main idea and summarization instruction on reading comprehension of expository text for alternative high school students. The lead researcher explicitly taught participants how to summarize expository passages. Participants were taught to generate a big idea topic of a passage, identify key words and phrases, locate or generate main ideas, and generate an oral summary. The three participants increased their performance on the researcher-developed oral summary measure and the summarization guide after receiving the reading comprehension intervention. Furthermore, participants felt they were able to learn how to summarize expository passages, perceived the intervention as effective, and that it helped their reading comprehension. Overall, results indicated that the intervention, which was explicit main idea and summarization instruction aimed to improve reading comprehension, is an effective practice for students who attend alternative high schools.