When and how does traditional culture hamper diffusion of knowledge and economic development? In this article, I use Catholicism in 19th-century France as an example of traditional culture, and focus on a crucial phase of modern economic growth, the Second Industrial Revolution (1870-1914). During this period, technology became skill-intensive, leading to the introduction of technical education in primary schools. I exploit spatial variation in intensity of Catholicism (i.e., religiosity) and show that more religious areas significantly lag behind after 1870, but not before. Schooling appears to be the key mechanism: I find a slower introduction of the technical curriculum and a push for religious education in more Catholic areas. Religious education, in turn, is negatively associated with industrial development about 10-15 years later, when school-aged children would enter the labor market, and this negative relationship is more pronounced in skill-intensive industrial sectors.