Attention Deficit Hyperactivity Disorder (ADHD) presents specific cognitive and attentional characteristics that can significantly affect web navigation and information processing. Despite the widespread adoption of the Web Content Accessibility Guidelines (WCAG), there is limited empirical evidence addressing their effectiveness for users with ADHD. This study evaluates the applicability of accessibility and usability guidelines through a set of controlled user tests conducted with adolescents diagnosed with combined ADHD. The tests assess multiple web design elements, including multimedia presentation, sound control, content layout, textual clarity, temporal elements, links, and iconography. These tests were adapted from previously validated experiments conducted with other neurodiverse users. Quantitative results were obtained by measuring task completion times, complemented by qualitative observations of user behavior. The findings reveal that certain guidelines significantly improve performance for users with ADHD, while others produce results that differ from standard WCAG recommendations. The results highlight the importance of considering the specific cognitive profile of users with ADHD and avoiding generalized accessibility assumptions. This study provides evidence-based design recommendations to support the development of more effective and inclusive web interfaces for this user group.