We define and advocate the subfield of educational software engineering (i.e., software engineering for education), which develops software engineering technologies (e.g., software testing and analysis, software analytics) for general educational tasks, going beyond educational tasks for software engineering. In this subfield, gaming technologies often play an important role together with software engineering technologies. We expect that researchers in educational software engineering would be among key players in the education domain and in the coming age of Massive Open Online Courses (MOOCs). Educational software engineering can and will contribute significant solutions to address various critical challenges in education especially MOOCs such as automatic grading, intelligent tutoring, problem generation, and plagiarism detection. In this position paper, we define educational software engineering and illustrate Pex for Fun (in short as Pex4Fun), one of our recent examples on leveraging software engineering and gaming technologies to address educational tasks on teaching and learning programming and software engineering skills.