The field of game design for educational content lacks a focus on methodologies that merge gameplay and learning. Existing methodologies typically fall short in three ways: they neglect the unfolding of gameplay through players' actions over a short period of time as a significant unit of analysis; they lack a common consideration of game and learning mechanics; and they falsely separate the acts of playing and learning. This paper recommends the gameplay loop methodology as a valuable tool for educational game design, as it addresses these major shortcomings. Furthermore, this paper outlines how this methodology can be supported by knowledge from subject-specific didactics--considering both the curriculum and its mediation (contributed by experts from educational practice) as well as methods of player-centered design--in order to ensure the appropriateness of learning objectives and techniques of mediation in the context of a particular field of knowledge, the game's appeal to its target group, and the effectiveness of the learning mechanics. A case study of the design and production phases of Antura and the Letters, a literacy game for Arabic refugee children, illustrates the uses of the gameplay loop methodology situated in the described broader approach to educational game design. Finally, this paper explains the results of an impact study revealing that the approach indeed provides the opportunity to merge playing and learning.