After the reform in 1962 Sweden had an educational system that mixed a certain amount of level grouping and theoretical and practical streams with social coherence in the sense that classes contained pupils opting for different alternatives in those respects. In the first part of the 1990s a series of rapid reforms entirely transformed Swedish education which, amongst other things, abolished all forms of differentiated teaching and different tracks. The new school is an entirely unitary school, underpinned by principles of inclusiveness. As such, the reforms are a remarkable example of reforms committed to ideological (in the wide sense) principles, which is testified by the way they were orchestrated and subsequently evaluated. To this day, there is a consensus within politics, top administration and academia th at any form of differentiation of levels or into tracks is detrimental at it stigmatize andperpetuate class society. The present study presents how the Swedish education was made to a completely unitary system in a series of intervention, ranging from a new grading system to a thoroughly redesigned teacher education. The main empirical contribution is a survey which display how teachers regard the effects of the different forms of heterogeneity at classroom level that often follow suit with a unitary school system. The effects of heterogeneity at the classroom level are a highly charged issue not only in Sweden and extent research is at best ambiguous regarding the effects. Teachers in theoretical subjects from lower and upper secondary schools were included (n=973, response rate 63 percent). The results show that heterogeneity is largest where the pupils are socio-economically disadvantaged. A large share of the teachersr eports that they find it difficult to fulfil the needs of both weak and strong pupils. Heterogeneity also seems to be connected to other aspects of the teachers working conditions, such as influence, tasks that are perceived as illegitimate and emotional strain. These results are finally discussed with reference to the ideological commitments that shaped the advent of these reforms and that still prevail.