Course‐based Undergraduate Research Experiences (CUREs) offer an inclusive means to engage students in the scientific process and enhance student learning gains and persistence in STEM. To realize the benefits of CURE implementation, is there a minimum length of CURE? We studied the learning and attitudinal outcomes of more than 1,000 undergraduate students across the United States involved in chemistry, biochemistry, and molecular biology CUREs using malate dehydrogenase as the model system. There were three conditions, complete semester CURE (cCURE), modular CURE of about six weeks in length embedded into a laboratory course (mCURE), and no CURE (control). We also looked at the impact these conditions had on students who are persons excluded from STEM due to ethnicity or race (PEER). We hypothesized that the longer the students spent in a CURE the better their outcomes. We measured student outcomes using several validated measures and compared the conditions using ANOVA, ANCOVA, and chi‐square analyses. We found cCURE students had higher experimental design learning and STEM support than control students. We found cCURE>mCURE>control for student’s report of their interest in conducting research in the future, support for STEM students, and their interest in a STEM career. Students in the cCURE and control had higher positive attitudes about scientific research than students in the mCURE. There were no differences between conditions for negative attitudes towards science, science literacy, and beliefs about learning science. We found PEER students reporting the same results as White/Asian students, except for their interest in conducting research: PEER students in mCUREs had higher interest than their White/Asian counterparts in conducting research. We conclude that the overall pattern was for students in the cCURE condition to have better learning and attitudinal outcomes than students in the mCURE and control conditions. Additionally, PEER student outcomes in CURE conditions were similar to their White/Asian counterparts. These results should encourage faculty to use CUREs in laboratory courses to improve all students’ outcomes and indicate that even a short CURE embedded within a traditional laboratory course can benefit students.