The growing trend in current thinking about urban forests as public health infrastructure has elevated the importance of trees in public health and urban greening policies and standards. Urban trees provide many ecosystem services along with psycho-socio-cultural, health, and economic benefits to humans.  Trees provide natural shade and protect humans from solar ultraviolet radiation, and have the potential to reduce UV exposure during childhood, especially with the recent emphasis on outdoor activity. Little quantitative data exist on how tree shading affects the penetration of solar erythemal UV radiation (i.e. erythema or skin burning). To date, most studies have focused on the measurement of UV-A radiation within Australian tree canopies, with few measuring UV-B radiations. As part of a broader effort to understand the shade value of trees for human health, we collected solar UV radiation exposure data beneath 64 individuals of 16 tree species commonly planted in the City of Toronto's schoolyards and public parks, using UV electronic logging dosimeters that have a spectral response closely matching the erythemal action spectrum. The dosimeters were placed under each tree using PVC tubes at the same height as a small child. The study was carried out daily during high exposure times. Results show differences among UV penetration beneath the crowns of different tree species. UV protection factor (PF: the ratio of open-site UV to below-canopy UV) varied 2.6-fold among species, ranging from 1.3−3.4. Statistical models for variation among trees indicated that crown transparency (%), the ratio of crown breadth to height to live crown, and species shade tolerance were important predictors of PF. We highlight the importance of urban shade trees for human health and provide information on choosing the best tree species for UV protection. These results can help inform tree management strategies and policies to increase UV protection in schoolyards and other public spaces.