Self-regulated learning (SRL) is an important aspect of successful knowledge acquisition. Adaptive learning technology (ALT) is a form of educational technology that can improve SRL by offering learners personalized and timely support. Despite the potential of ALT to support SRL, its integration into schools' pedagogical practices remains a challenge. To address this challenge, this study took a co-design approach to develop and implement an ALT in an upper secondary school over three phases. In the exploration phase, we collected and analyzed qualitative data from structured interviews (n = 14) and group discussions (n = 7) with students and teachers. In the defining phase, we identified problem areas of ALT through a co-design group and formulated suggestions for developments. These suggestions were integrated into the ALT in the shaping phase. The findings showed that the co-design process facilitated better incorporation of the needs of students and teachers into the development of the ALT. Direct integration of user perceptions and descriptions strengthened the connection between ALT and SRL while enhancing the tool's adaptability. Not all suggestions from the co-design group could be implemented into the ALT. In the future, more attention should be given to understanding the interfaces between different groups of actors in the co-design process, particularly in K-12 education contexts.