Improving educational practice through reflection is one important focus of teacher professional development approaches. However, such teacher reflection operates under practical classroom constraints that make it happen infrequently, including the reliance on disruptive peer/supervisor observations or recordings. This article describes three design-based research iterations towards technological support for teacher reflection based on everyday evidence and feedback. The authors collaborated with 16 teachers from two different secondary schools, using a variety of prototype technologies (from paper prototypes to web applications and wearable sensors). The iterative evaluation of such prototypes led them from a high-tech focused approach to a more nuanced socio-technical one, based on lightweight technologies and 'envelope routines' that also involve students. After illustrating the potential of this approach to change teacher practice and students' learning experience, the authors also present a series of guidelines for the design of technology that supports such reflection based on everyday evidence gathering.