Every teacher has seen it happen. The first bell rings, and some students are tardy while others look half-awake. Then, just as the day seems to hit its stride, attention begins to drift again after lunch. While these periods of reduced focus are often accepted as an unavoidable part of school life, research suggests they are linked to predictable biological rhythms that may be mitigated by healthy exposure to blue-sky light. Indeed, improved classroom lighting may be one of the most practical tools schools have for boosting cognitive performance.