New societal demands call for schools to train students' collaboration skills. However, research thus far has focused mainly on promoting collaboration to facilitate knowledge acquisition and has rarely provided insight into how to train students' collaboration skills. This study demonstrates the positive effects on the quality of students' collaboration and their knowledge acquisition of an instructional approach that consists of conventional instruction and an online tool that fosters students' joint reflection on their collaborative behavior by employing self- and peer assessment and goal setting. Both the instruction and the collaboration reflection tool were designed to promote students' awareness of effective collaboration characteristics (the RIDE rules) and their own collaborative behavior. First-year technical vocational students (N = 198, M[subscript age] = 17.7 years) worked in heterogeneous triads in a computer-supported collaborative learning environment (CSCL) on topics concerning electricity. They received either 1) conventional instruction about collaboration and the online collaboration reflection tool, 2) collaboration instruction only, or 3) no collaboration instruction and no tool. Analysis of chat data (n = 92) and knowledge tests (n = 87) showed that students from the instruction with tool condition outperformed the other students as far as their collaborative behavior and their domain knowledge gains.