The present paper is about the author's current research on children's education in urban contexts. It departs from the rising offer of programmes for school children in out-of-school contexts (e.g. museums, libraries, science centres). It asks what makes these practices educational (and not just interesting, entertaining and/or audience building). Based on Biesta (2006a, 2010) theory of education, the author frames and analyses the educational characteristics of, and possibilities of articulating, in and out-of-school educational practices. This paper aims at understanding if the occasional outing from primary school premises promotes interruptions in the humanist foundations of school. In order to analyse relations between different institutions and professionals (to be) engaged in educational activities and programmes, Novoa (2002, 2009) essays will be brought to the discussion, namely his conception of the "Public Space of Education"--as a space where culture, education, arts, sports and leisure are shared responsibilities, and where diverse institutions are networked aiming towards societal pluralism. I argue for the possibility of using cities' public spaces as contexts with a worldly quality to complexify children's education. Nevertheless, I draw attention to the unbearable educational lightness that these practices may carry if they do not go beyond the praise of chance; as well as to their unsustainable weight if they perpetually repeat school's normal orders and add up rational discourses.