The purpose of this study was to understand how teachers participate in collaborative professional development in order to implement a reform-based unit. The motivating question for this study was: How do teachers implement a reform-based unit which includes an innovation cluster of emerging online technologies and a unit design framework for a constructivist-based learning environment? The study participants were four teachers who implemented an online authentic problem-solving unit, Improving Interstate 70, simultaneously in 4th and 5th grades in four different school districts, urban, rural, suburban and a small city in the USA. The data collection process used interpretive research practices to capture the dynamics and complexity of learning processes throughout the professional development of the teachers. Using Cultural Historical Activity Theory the researcher was able to define aspects of the collaborative professional development processes that impacted the implementation of these collaborative online constructivist problem-based learning units.