Professions like engineering were a vehicle for social mobility in Australia early in the twentieth century. By the late twentieth century, despite considerable expansions in higher education, it was much harder for young people to enter a trade and then to use their skills and experience to move into professional engineering. The shift in occupation structure in the early twentieth century, when professions - including engineering - grew rapidly, gave new opportunities to working-class tradespeople to move into professional employment. After the 1960s, when educational norms standardised and professional knowledge became more complex, these pathways narrowed. Motor mechanics, for example, were “trade” engineers who were able to move into professional engineering early in the twentieth century in ways that were extensively limited by the end of the century. This article uses engineering as a case study to consider institutional changes, including the growth of middle-class unions and the increased share of education carried by Australian universities, which made access to professional occupations more difficult for working-class tradespeople from the 1960s onwards. This helps us to identify the emergence of a new kind of class solidarity among professionals in the mid-twentieth century, with which they developed strategies to win rights for themselves, but sometimes at the expense of working-class interests.