Objective: In the general population, attention is reliably enhanced after exposure to certain physical environments, particularly natural environments. This study examined the impacts of environments on attention in children with ADHD. Method: In this within subjects design, each participant experienced each of three treatments (environments) in single blind controlled trials. Seventeen children 7 to 12 years old professionally diagnosed with ADHD experienced each of three environments--a city park and two other well-kept urban settings--via individually guided 20-minute walks. Environments were experienced 1 week apart, with randomized assignment to treatment order. After each walk, concentration was measured using Digit Span Backwards. Results: Children with ADHD concentrated better after the walk in the park than after the downtown walk (p = 0.0229) or the neighborhood walk (p = 0.0072). Effect sizes were substantial (Cohen's d =0.52 and 0.77, respectively) and comparable to those reported for recent formulations of methylphenidate. Conclusion: Twenty minutes in a park setting was sufficient to elevate attention performance relative to the same amount of time in other settings. These findings indicate that environments can enhance attention not only in the general population but also in ADHD populations. "Doses of nature" might serve as a safe, inexpensive, widely accessible new tool in the tool kit for managing ADHD symptoms. (Contains 1 figure and 1 table.)