## 2 Materials and Methods
### Procedure  
The study was approved by the Institutional Review Board of the Universitat Internacional de Catalunya (PSI-2023-04), and all data were de-identified to ensure participant confidentiality. The research team and the school psychology team conducted presentations with families and participants to inform them of the study procedures and assessments. In addition, and in accordance with Spanish law, legal guardians signed informed consent forms for all interested participants. The study used a convenience sampling method in which students who voluntarily expressed interest in participating were screened to deter mine eligibility. Researchers, together with the school psychologist, determined participant suitability using an eligibility checklist.  
Those participants who met the eligibility criteria were randomly assigned to either the experimental group (\(n=22\)), which received the gamified VR program Enhance VR by Virtuleap, or the active control group (\(n=16\)), which received a comparable VR nature-based relaxation training.  
Interventions  
The experimental and control interventions were conducted over five weeks, with sessions held twice a week for 30 min each, for a total of 10 sessions per participant, aligned with similar research parameters [56]. Each participant was provided with an individual standalone VR Meta Quest 3 headset (Meta, Menlo Park, CA, USA). Interventions were delivered face-to-face in groups of four to six participants under the supervision of a mental health professional with a master's or doctoral degree. Study completion was defined as participants attending at least 80% of the scheduled sessions. At the end of the interventions, all participants in both the experimental and control conditions completed at least 90% of the sessions.  
The experimental group used the Enhance VR software (v.2.7.0.0, Virtuleap, Lisbon, Portugal) [56; 57], a gamified VR cognitive training that consisted of six games (two games per session) designed to target specific cognitive functions. Some of these games were previously validated in an adult sample with Attention-Deficit/Hyperactivity Disorder [56], and it was decided to use games that target very similar cognitive constructs. For example, one game focused on cognitive flexibility, requiring participants to quickly switch between different tasks and problem-solving strategies. Another game centered on planning, asked participants to make a series of decisions to achieve a specific goal. Other games engaged targeted working memory, divided and sustained attention, and processing speed. All the games involved adapted the difficulty level to the user's performance. To assess the user's initial level of performance, each game session began with a baseline session. Subsequent sessions resumed from the user's most recent skill level, allowing for individual progression. A detailed description of the sessions and the content of each game is shown in Figure 1.  
Figure 1: Brief description of the games included in the VR cognitive training program (experimental condition).  
The active control group used the Nature-Trek VR software (v.1.27, Greener Games Company, Telford, UK), which simulates natural environments like tropical islands, forests, lakes, and snowy landscapes over 10 sessions, each featuring a different environment. In the first session, there was a brief training of the VR environment (training stage), then participants personalized their virtual environment by adding elements such as trees and changing the weather, and selecting their preferred navigation method, such as teleportation or arm swing locomotion(tailor stage); then, they engaged in structured deep breathing exercises with a visual aid to promote relaxation (deep breathing stage), and in the last 6 min, participants were relaxed and immersed themselves in the virtual environment, exploring and identifying personal relaxation strategies without specific instructions or visual cues (immerse stage).