As emerging technologies become increasingly inexpensive and robust, there is an exciting opportunity to move beyond general purpose computing platforms to realize a new generation of K-12 technology-based learning environments. Mixed-reality technologies integrate real world components with interactive digital media to offer new potential to combine best practices in traditional science learning with the powerful affordances of audio/visual simulations. This paper introduces the realization of a learning environment called SMALLab, the Situated Multimedia Arts Learning Laboratory. We present a recent teaching experiment for high school chemistry students. A mix of qualitative and quantitative research documents the efficacy of this approach for students and teachers. We conclude that mixed-reality learning is viable in mainstream high school classrooms and that students can achieve significant learning gains when this technology is co-designed with educators.