This full research category paper reports the result of an experiment that designed and implemented peer code review (PCR) to help introductory computer science (CS1) students understand programming concepts and improve their programming skills. Instructors at North Dakota State University have observed that students enrolled in CS1 programming course experience difficulty understanding programming concepts. We performed an empirical study that evaluated if PCR can help address the problem. We analyzed data collected from the PCR session, code development activity and end-of-study questionnaire. Our result provides insights into the most and least reported error types. Students were able to systematically improve the review output. More importantly, PCR had a significant positive impact on students' performance when developing their own code. PCR can be an effective teaching tool that when used in CS1 programming course can improve students' understanding of programming concepts and improve their programming skills.