Integrating digital technology in education is challenging. This study reports on three high school mathematics classes where teachers attempted to improve their teaching and student learning by using a digital tool. For analysis we use the Information System Artifact model Lee et al. (2015) which distinguishes between three integrated sub-artifacts, the technological, the informational and the social and the Structurational Practice Lens to educational technology Halperin (2017). Using interviews and observations we find the major obstacle for student learning is a less developed social artifact. Students have difficulties using the tool effectively when teachers do not work to develop shared practices in technology use. When teachers do not themselves use the tool actively, they do not fully understand how students can learn from it, neither can they help them in synthesizing teacher- and tool instructions. Students end up having "two masters" competing rather than integrated teacher instruction and technology assistance.