The sharing of a principal’s position by two people on equal footing is described as a way of decreasing an often heavy burden and as favourable to principals and schools. However, when Sweden’s current Education Act (2010:800) became operative in 2011, it wetblanketed the issue of shared principalship. The act states the principle of singularity in that there must be a person with the title of principal in each, so-called, school unit and that this principal must be one. Thereby the collaborative potential of joint principalship (i.e. complete cooperation, where formal hierarchic equality is in place and work tasks are merged) was extinguished. This paper aims to shed light on how and why this prohibition was introduced in the legislative process. The fact that the prohibition of joint principalship came into effect may be understood as a con­sequence of the length, forms of work, extent and political prestige of the legislative process; shared leadership was at most a marginal issue. In the cathedral-building project there was no intent to question traditional ideas about leadership. The important lines of argument concerned lack of trust in the way the municipalities organised their schools. Therefore, there was a wish for increased direct state control by going via the principals as the appointed responsible authority., This, together with the late invented school unit concept had unforeseen effects for the organising of the principal’s position. The principle of singularity ruled and a ban on joint leadership was the consequence – with­out consideration whether this favoured the overarching aim of the law: increased pedagogical re­sponsibility and leadership with a focus on the students’ learning, results and democratic upbringing.