This systematic literature review examines how digital technology influences student well-being and the implications for teacher professional development, following PRISMA 2020 guidelines to ensure rigour and transparency. Six databases, including ScienceDirect, ERIC, and Scopus, were searched using a PICOS framework focusing on students and educators, digital well-being interventions, and cognitive, social, emotional, and behavioural outcomes. From 474 initial records, 50 peer-reviewed empirical studies (2020–2025) met the inclusion criteria after multi-stage screening in Covidence, with an inter-rater reliability of κ = 0.76. Thematic synthesis identified both negative impacts, such as anxiety, sleep disruption, attention difficulties, and academic decline, and positive outcomes, including emotional coping, resilience-building, and informal learning. Effective school-based interventions ranged from curriculum-integrated programmes to mindfulness, screen-reduction initiatives, and culturally adapted approaches, yet implementation remains inconsistent. Major barriers include limited teacher training, weak measurement tools, policy fragmentation, and digital inequality. The review concludes that embedding digital well-being within sustained, evidence-informed teacher professional development is essential for equipping educators to address students’ evolving digital experiences and to implement whole-school digital well-being strategies.