Table 2.

Corresponding criteria of the GameFlow element challenge and their implementation and fulfillment in the story game.

Challenge criteria	Implementation in the story game	Fulfillment status
Challenges are adjusted to players’ skills	As the research group selected age-appropriate stories and invented literal questions that were supposed to match the cognitive skills of kindergarten children aged 5 years and as the virtual hub world and avatar customization system appeared self-explanatory without any form of written language, we concluded that the game tasks were adapted to the skills of the target prereading age group.	Yes
Challenges are player-adjusted	The selection and the order of the stories, along with their corresponding content-related questions, were fixed and the same for all players. Moreover, although we have no direct proof of the stability of the difficulty of the stories and questions, the game was originally not designed to increase in difficulty. In that sense, we concluded that the challenge levels were not individually adapted and did not increase along with progress in player skills.	No
Challenge levels increase to improve the players’ skills	The selection and the order of the stories, along with their corresponding content-related questions, were fixed and the same for all players. Moreover, although we have no direct proof of the stability of the difficulty of the stories and questions, the game was originally not designed to increase in difficulty. In that sense, we concluded that the challenge levels were not individually adapted and did not increase along with progress in player skills.	No
The game provides new challenges at appropriate times	Although not directly tested, we assumed that the difficulty level of the stories, the questions, and other tasks remained relatively stable throughout the game. However, book series and storytellers switched every 4 sessions. This required adaptability and possibly formed a new challenge for some (but not all) players.	Partly