This case study investigates an experienced secondary school mathematics teacher's understanding of mathematics ("her" math) and decisions she makes about her students' classroom experiences ("their" math). This report focuses on the competing roles of the teacher's growing understanding of novel technology-rich mathematics and her decisions about activities and expectations in an algebra course in light of her beliefs about learning and teaching. Data document developments in her mathematical understanding and classroom practice during her first 13 months of teaching Computer-Intensive Algebra as a participant in the Empowering Secondary Mathematics Teachers in Computer-Intensive Environments project (CIME). (Author)