Community colleges play a vital role in postsecondary education, enrolling more than one in every three postsecondary students. While their importance has grown over the past 50 years, their students' success rates remain low. Consequently, community college stakeholders are searching with mounting urgency for approaches that increase students' success rates. "Learning communities" are one popular strategy. This article describes the results of one of the largest (n ˜ 7,000) independent randomized trials in higher education history--an evaluation of the effectiveness of learning communities for students in developmental education at six community colleges throughout the United States. The estimated overall average effects of learning communities are positive, although quite modest.