There has been a call for reform in the teaching and learning of mathematics that requires moving away from passive student learning and memorization to active participation and exploration; however, mathematics teaching in American classrooms remains largely traditional. A methods/practicum sequence provides a unique opportunity to actively instill an understanding of tasks that promote the mathematical practices. Moreover, planning and implementing worthwhile mathematical tasks requires and demonstrates mathematical knowledge for teaching. The mixed-methods case study was designed to determine the effects of a task-based methods/practicum sequence on secondary mathematics teacher candidates’ ability to plan for and enact worthwhile mathematical tasks. The treatment was guided by Implementing Standards-Based Mathematics Instruction: A Casebook for Professional Development, authored by the leading researchers on mathematical instructional tasks. The Instructional Quality Assessment (IQA) was used to assess the potential and implemented cognitive demand of tasks used for instruction. The Mathematical Classroom Observation Protocol for Practices (MCOP²) was used to assess the mathematical practices that were observed during the same instruction. Participant reflections and interactions provided qualitative data to enhance the quantitative findings. It was found that scores on both assessments increased significantly from the beginning to the end of the semester. Moreover, the participants expressed greater awareness of tasks and teaching strategies that maintain their cognitive demand. These findings add to what is known about secondary mathematics teachers’ mathematical knowledge for teaching as well as establish a relationship between the IQA and MCOP² as it pertains to the study.