Connected comprehensive-school systems were developed and expanded in all Nordic countries during the twentieth century. In the Nordic context, the term refers to unified, un-streamed age-based schools catering for all pupils regardless of academic and socio-economic background and resources. The Nordic comprehensive model further implies both theoretical and practical training and should, in principle, provide pupils with the same structural opportunities for learning in terms of teacher competence, class size, text materials and other sources of support. The school system incorporates primary and lower secondary levels (1–6/7 and 7–9/10) in all five countries.