Despite the growing research base on preservice teacher noticing of children's mathematical thinking in video, few, if any studies consider the complex nature of the video representations themselves. Drawing from cognitive load theory, we developed a rubric to code the complexity of the salient teaching and learning events captured in video, and analyzed the relationship between video complexity and preservice teacher (n = 233) noticing. Results indicate that two categories significantly

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... ht children's mathematical thinking and two categories significantly mask children's mathematical thinking for preservice teachers. We discuss the implications of these results for the design of our instructional platform and other video-based learning environments used in preservice teacher education settings.