## 4 Method
### Procedure and Material  
The three experiments that took place in the classrooms of three different primary schools lasted 45 min, while the duration of the experiment conducted in the university lecture hall was 90 min since university students had to evaluate all three AR apps (Figure 27). Regarding the first three experiments, pupils were randomly assigned to dyads, and with the help of the researchers, the AR app was installed on schools' ICT equipment such as Android mobile devices. Then, the instructors (teachers) gave a relevant introductory stimulus. Next, the pupils opened the AR Geography game, and according to the game's specifications, they had to scan either a QR Code or an image. After scanning, they played the game and, in the end, appropriate feedback was given to them according to their performance. Regarding the 5 th grade AR app, the game that was chosen was the \"Types of maps\" where the pupils had to answer a quiz with random questions that refer to the different types of maps. For the 6 th grade AR app: Earth as a living space for humans, the game \"Continents\" was chosen where an air balloon travels to different countries, and information regarding these countries is displayed. Finally, for the last AR app for the 6 th grade: Earth as a celestial body, the game \"Atmosphere\" was chosen, where the pupils had to place the layers of the atmosphere in the correct order. At the end, pupils had the opportunity to discuss what they have learned with their instructors (teachers).  
The procedure of the experiment that was conducted in the university lecture hall was the same, with the difference that there was neither introductory stimulus, nor instructors, and that university students played and evaluated all three AR apps, one after the other.  
After each experiment was completed, a questionnaire was given to all participants in printed form to evaluate the corresponding AR app. The questionnaire, also known as the System Usability Scale (SUS) is a state-of-the-art method in the user interface design field [35] and includes 10 questions to evaluate the usability of apps. The questionnaire uses a Likert scale of 1 (Strongly Disagree) to 5 (Strongly Agree) and the Greek version of it was used [36]. To calculate the overall SUS score, firstly the total score for all odd-numbered questions is added and then 5 is subtracted from the total to get (X). Next, the total score for all even-numbered questions is added and then that total is subtracted from 25 to get (Y). Finally, the total score of the new values (X + Y) is added and multiplied by 2.5 to convert the original scores of 0-40 to 0-100. Following these steps, the scores of participants for each question are converted to a number. Though the scores are 0-100, these are not percentages and should be considered only in terms of their percentile ranking. Based on the literature, SUS scores above 70 are considered above average and are acceptable, and anything below 70 is below average. According to the grading scale, SUS scores that are below 60 are considered as an \"F\", between 60 and 69 as a \"D\", between 70 and 79 as a \"C\", between 80 and 89 as a \"B\", and 90 and above as an \"A\" [37; 38; 39].  
In addition, one more question was added to measure whether the proposed AR Geography apps look like games or not. Finally, apart from the questionnaire, data were also collected through personal observation occurred by the researchers throughout participants' interaction with the AR apps.  
Figure 27: Pupils in primary school (**left**) and university students (**right**) evaluate the AR apps.