A core mechanism of unified growth theory is that accelerating technological progress induces mass education and, through interaction with child quantity‐quality substitution, a decline in fertility. Using unique new data for 21 OECD countries over the period 1750–2000, we test, for the first time, the validity of this core mechanism of unified growth theory. We measure a country's technological progress as patents per capita, R&D intensity, and investment in machinery, equipment, and intellectual property products. While controlling for confounders, such as income growth, mortality, and the gender wage gap, we establish (1) a significant impact of technological progress on education (positive) and fertility (negative); (2) that accelerating technological progress stimulated the fertility transition; and (3) that the baseline results are supported in 2SLS regressions using genetic‐distance weighted foreign patent‐intensity, compulsory schooling years, and minimum working age as instruments.