Karen Koellner's research focuses are on mathematics teacher learning and students' mathematical thinking. Currently, Koellner is studying the impact of professional development on teachers' knowledge, instructional practices and student achievement, as well as the scalability and sustainability of professional development models in schools and districts. Koellner has served as an associate professor of mathematics education at the University of Colorado Denver and as an assistant professor at Georgia State University. She has served as co principal investigator on two large projects one funded through the National Science Foundation (NSF)(2008-2012) and the other through the Institute for Economic Research on Innovation (IERI)(2003-2007). She was awarded the UCD Distinguished Research Award in 2009. Koellner earned her doctorate in mathematics education from the Arizona State University in 1998.