Iran’s period total fertility fell sharply from 7 children per woman in the mid-1980s to replacement level in less than two decades. The fertility decline was ubiquitous across all age and social groups and all geographic settings, but it was the better educated women who first experienced a shift to a low fertility level. We investigate fertility trends by education from a cohort perspective to gain a deeper understanding of the role of education expansion for fertility decline. Using data from the 2006 and 2011 censuses, we found that fertility fell rapidly among women born in the 1950s and 1960s. The fall in fertility was mostly driven by reductions in the progression ratios to the third and subsequent births in the first stage, and later by an increase of childlessness and a strengthening orientation towards a two-child family pattern. Despite the observed fertility decline among all education groups, education differences remained strong across all the analyzed cohorts. Women with upper secondary and higher education show a shift towards a small family size, a clear dominance of a two-child family pattern, but also a rise in the share with only one child and a rapid increase in childlessness due to non-marriage. Increasing level of education has strongly contributed to the observed fertility decline, although among the women born in the late 1950s and in the 1960s the effect of falling fertility at all education categories clearly dominated over the structural effect of education expansion. As more women have continued reaching tertiary education in the last two decades, the adoption of small family size and the rise of non-marriage and childlessness are likely to accelerate among the women born in the 1970s and 1980s.