This study investigated the effects of Discovery Learning Scientific Community Laboratories (DL-SCL) and traditional non-DLSCL laboratories on students' conceptual understanding in a Physics-1 lab. At many universities, physics programs use a traditional lab style, despite research on the benefits for reform-oriented physics labs. This DL-SCL approach included features of "inquiry-based learning" (e.g., students generated hypotheses and designed experiments) and "scientific community labs" (e.g., students discussed designs and findings). This study used a quasi-experimental design with quantitative-method data collection and analysis procedures. Twelve sections of a Physics I lab were assigned to two groups: Treatment (DL-SCL) and Control (non-DLSCL). In Treatment and Control sections, conceptual understanding was measured pre/post using the Mechanics Baseline Test (MBT) and the Force Concept Inventory (FCI). Study findings indicated that DL-SCL approach in teaching Physics Lab-1 significantly improved students' conceptual understanding.