English language learners are one of the largest groups of students who struggle with literacy in general and comprehension in particular. What makes scaffolding so effective is that it enables a teacher to keep a task whole, while students learn to understand and manage the parts and presents the learner with just the right challenge. In so doing, it helps students to cope with the complexity of tasks in an authentic manner (Pearson, 1996).This study is conducted in order to understand to what extent Iranian high school teachers' scaffolding has an effect on learners' reading comprehension. First-grade high school teachers were selected, in order to be observed for answering the question. {\textcopyright} 2011 Published by Elsevier Ltd.