Many labour organizations that sponsor occupational health and safety training champion "peer training," preferring instructors drawn from the shopfloor over academically credentialed experts. But peer training is hardly new: in the skilled trades, master craftsmen have instructed apprentices since the Middle Ages. Building on the apprenticeship model of education, the U.S.-based construction unions have created a network of more than 4,000 peer trainers who provide occupational health and safety training to up to 100,000 men and women in the building trades each year.