Dutch prescriptive grammar rules dictate that the complementizer dan ‘than’ should be used in comparative constructions of inequality. This has been an issue for grammarians from the sixteenth century onwards when als ‘as’ started to be used as an alternative form in this type of context. In order to find out why and when people choose one comparative marker over the other, we examined the use of these markers in the Spoken Dutch Corpus (CGN). We found that the use of dan is overall more common than als in comparative constructions of inequality, even though from a linguistic point of view als might be favoured. The choice between als and dan turns out to be strongly correlated with the level of education. Although this factor has been assumed to be of influence for a long time, as far as we know it has never been quantitatively tested before. We conclude that the effect of the level of education we found reflects the strong influence of the prescriptive rule taught in schools, repressing the use of als in comparatives of inequality.