Teaching and learning programming, and especially Object-Oriented Programming (OOP), is a complicated and challenging task. Students have to comprehend various OOP concepts and utilize them for designing object-oriented programs. Various types of educational programming environments, such as microworlds and educational games, have been devised for supporting novices mainly in comprehending OOP concepts. However, such environments do not usually support students in the conceptual design of object-oriented programs of a considerable length and complexity. In this paper, we focus on a systematic mapping study (SMS) of educational programming environments for enhancing the conceptual design in OOP, which relies on modularity, abstraction and encapsulation. The research questions investigate the intended learning outcomes, the empirical evidence on the effectiveness, and the teaching/learning technologies used by educational programming environments for enhancing the conceptual design in OOP. The findings can support instructors in selecting appropriate tools for their courses and researchers in the field of educational programming environments for OOP.