This paper focuses on the physiological identification of Clutch-Flow states in real-world educational scenarios. By using the Eduflow scale and Polar H10 wearable devices, we develop two STEAM face-to-face project-base teaching-learning experiences with students in 5th and 6th grade of primary education. Based on Heart Rate Variation (HRV) recorded for 18 one-hour sessions and their comparison to responses obtained in 181 EduFlow questionaries filled in by students after each session, a Kubios-based analysis was performed, obtaining a total of 127 reports about HVR. The main findings of this study reveal multiple and meaningful correlations between physiological data and the flow phenomenology in group of students; and a proposal to identify clutch states based on the EduFlow scale results.