A convention in New Zealand historiography is that the electoral fortunes of the Labour Party in the first half of the twentieth century were tightly constrained by a particular structure of cleavage. Although by 1919 or 1922 Labour had won the support of the vast majority of urban working-class voters in the leading towns, it could not win office with their support alone. This was demonstrated in the 1930s when it gained electoral domination by winning over small farmers and the urban middle classes; and after the late 1930s when the support of non-manuals ebbed away and it lost office in 1949. This article tests the convention. It takes the ten largest provincial towns, determines the class composition of their streets in 11 general elections, estimates the distribution of the votes for each party in each street in each town for every year, and correlates the estimated percentages of Labour vote with percentage of working class. The results are the inverse of the trends claimed by the historiography. The article then examines the social geography of the towns and finds systematic evidence of an unexpected cleavage inside the working class: skilled workers had a much weaker tendency to vote Labour than the unskilled and no tendency at all to reside in the same residential areas as the unskilled.