A design research study was conducted over two years with 20 second grade students who are part of the Measure Up (MU) research and development project underway at the University of Hawai'i. Students were asked to count in multiple bases. After doing so, they were asked how they knew when to go to a new place value and why it was necessary. All 20 students demonstrated skill in counting and representing the numbers, but analysis of their responses revealed different levels of generalization of method and explanation of underlying principles.