Various forms of public-private collaborative organizations have been emerging in the education sector, a development that has made managing public-private partnerships an unavoidable imperative for school managers today. Addressing interactions between the partnership manager of and partners in a public-private innovation partnership, this article explores the attachments public and private actors establish in the framework of such partnerships. While formal structures often bind partnerships together, open innovation partnerships have a more fluid organization in which the participants have to establish the ground for their common work. Specifically, the article presents a study of a Danish partnership project aimed at developing a new secondary school. Drawing on the sociology of engagements, the article sketches out the differing forms of mutual engagements at stake between the actors involved and the challenges they face. As the partnership studied lacked formal agreements, the manager's and partners' locally performed acts of proximity became a means of binding the partnership together. In these acts, a mutual explorative engagement intertwined with a familiar engagement, thus creating a distinct attachment of familiar strangers between the public and private actors -- an attachment through which ideas on education and common educational visions could traverse the public and private sectors.