This study applied design research in designing a mobile-device-supported interactive writing platform (ePoetry Zone, ePZ) for elementary EFL learners in collaborative creation. In the first iteration essential supports needed in interactive writing were identified and became the design foundation of the mobile interactive writing platform (ePZ). In the second iteration, ePZ was developed and then 23 fourth graders participated in collaborative creation by using ePZ. Some problems found in a traditional EFL setting were solved but other new problems were identified as well. The findings of the second iteration were collected and served as the revising foundation of the current version of ePZ (ePZ II).