This paper examines two activities in a weeklong Professional Development (PD) focused on implementing mathematical play in kindergarten classrooms. Though the weekly activities all had different goals, the two focal activities (Pattern Blocks and Create-a-Monster) were designed specifically to be both playful and mathematically engaging for the kindergarten teachers taking part in the PD. This analysis looks at why Create-a-Monster fell short of those goals and compares it to the more successful Pattern Blocks to better understand how to design activities that are playful and mathematically interesting activity for early elementary educators. We finish with implications and future directions on playful PD design. [For the complete proceedings, see ED657822.]