Table 3.

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

Player skills criteria	Implementation in the story game	Fulfillment status
The game is playable without an instructive manual	Although the research group provided a short manual for the players’ parents or caregivers, the game was designed in a way that children aged 5 years could pass the first and following sessions without any form of explanation. Game mechanics were easy to use, transfers from one game mode to another occurred automatically, and as the target group was considered prereading, there was no form of written text implemented in the game.	Yes
Learning the game is not boring	A learning phase or tutorial game was not implemented, as game sessions were self-explanatory, and players learned to play by doing. When opening the application on the tablet for the first time, players gained enough information on how to progress. Hence, we believed that this criterion did not necessarily need to be implemented.	No
Absorbing tutorial games should teach players how to play the game	A learning phase or tutorial game was not implemented, as game sessions were self-explanatory, and players learned to play by doing. When opening the application on the tablet for the first time, players gained enough information on how to progress. Hence, we believed that this criterion did not necessarily need to be implemented.	No
Web-based help is provided for players in need	The research group did not provide a web-based help service tool. However, parents or caregivers could contact the research group via email or telephone anytime in case of technical or motivational problems. If necessary, a member of the research group visited the players at home to fix possible technical or player-related problems.	Partly
Skill progress occurs gradually at an appropriate pace	Although not directly tested, we assumed that the difficulty level of the questions and other tasks remained relatively stable throughout the game and that they were adapted to the target age. The game did not primarily intend to specifically improve language comprehension (measured based on mean question response accuracy per game phase) of the target group. However, it is possible that for some of the players, mean question response accuracy would gradually increase with higher story game exposure. This will be explored in this paper.	Partly
Skill effort and development is rewarded	Skill effort was rewarded by means of stars. After finishing a session, regardless of whether the responses to the content-related questions were correct or not, all players earned a star, which appeared on a stage in the virtual hub world and indicated the players’ progress in the game. Skill development was rewarded with coins, such that the more correct responses were given, the more coins were earned.	Yes
Game mechanics and interface are simple and easy to apply	All actions required the use of a touch screen, as the game was tablet based. Nowadays, in Western society, most children aged 5 years are familiar with these devices. Furthermore, players only had a limited set of actions, as advanced game options were locked with a password. These limited actions (eg, stopping, starting, or continuing the story game; selecting a response for the questions; buying accessories in the avatar customization system) were all self-explanatory (eg, selecting the correct response or a desired accessory by touch screen) or assigned with clear symbols on the screen (red arrow to stop the game and large green play symbol to start or continue the story recording).	Yes