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An important dimension of classroom group dynamics & collaboration is how much each person contributes to the discussion. With the goal of distinguishing teachers' speech from children's speech and measuring how much each student speaks, we have investigated how automatic speaker diarization can be built to handle real-world classroom group discussions. We examined key design considerations such as the level of granularity of speaker assignment, speech enhancement techniques, voice activity detection, and embedding assignment methods to find an effective configuration. The best speaker diarization system we found was based on the ECAPA-TDNN speaker embedding model and used Whisper automatic speech recognition to identify speech segments. The diarization error rate (DER) in challenging noisy spontaneous classroom data was around 34%, and the correlations of estimated vs. human annotations of how much each student spoke reached 0.62. The accuracy of distinguishing teachers' speech from children's speech was 69.17%. We evaluated the system for potential accuracy bias across people of different skin tones and genders and found that the accuracy did not show statistically significantly differences across either dimension. Thus, the presented diarization system has potential to benefit educational research and to provide teachers and students with useful feedback to better understand their classroom dynamics.