Although yes/no questions are one of the most frequently occurring question types in English, research on the development and production of yes/no questions-in particular in young English learners-is still very limited. For example, we know very little about potential errors young L2 learners make when they produce yes/no questions-an area that is crucial in order to provide useful feedback in different learning environments, including computer-based applications. This paper reports on an exploratory study conducted with Can you guess who I am?, an interactive, spoken-dialogue-based speaking activity that allows young English learners to practice yes/no questions. After introducing the SDS-based speaking activity, we present the findings from a systematic investigation of the output produced by 27 young English learners in Germany (ages 9-11) who engaged with the activity. A particular focus in the analysis was placed on the types of yes/no questions elicited and the types of errors made by the young learners. The findings provide further empirical support for a six-stage framework for the development of question formation in L2 learners [14]. Moreover, they offer insights into the types of errors young EFL learners make in forming polar interrogatives such as systematic confusion with regard to the auxiliaries "to be" and "to do". The findings are discussed in terms of (a) how they contribute to a more comprehensive understanding of young learner's speech and (b) how they will be used to inform further development of more targeted feedback options that can be implemented into the SDSbased speaking activity in order to harness its full potential for L2 learning.