The aim of this study was to investigate how reciprocal peer assessment in modeling-based learning can serve as a learning tool for secondary school learners in a physics course. The participants were 22 upper secondary school students from a gymnasium in Switzerland. They were asked to model additive and subtractive color mixing in groups of two, after having completed hands-on experiments in the laboratory. Then, they submitted their models and anonymously assessed the model of another peer group. The students were given a four-point rating scale with pre-specified assessment criteria, while enacting the peer-assessor role. After implementation of the peer assessment, students, as peer assessees, were allowed to revise their models. They were also asked to complete a short questionnaire, reflecting on their revisions. Data were collected by (i) peer-feedback reports, (ii) students' initial and revised models, (iii) post-instructional interviews with students, and (iv) students' responses to open-ended questions. The data were analyzed qualitatively and then quantitatively. The results revealed that, after enactment of the peer assessment, students' revisions of their models reflected a higher level of attainment toward their model-construction practices and a better conceptual understanding of additive and subtractive color mixing. The findings of this study suggest that reciprocal peer assessment, in which students experience both the role of assessor and assessee, facilitates students' learning in science. Based on our findings, further research directions are suggested with respect to novel approaches to peer assessment for developing students' modeling competence in science learning.