Mixed age classes has been a part of the Swedish education system from its beginning and used to be its norm. During the 1970’s the practice of having mixed age classes saw a new spring as it was deemed to have educational advantages, and since then there has been an ongoing debate among teachers, researchers, parents and politicians regarding how, and in what way, the advantages actually manifest themselves. Earlier research shows different results where some scholars find that mixed age classes have a negative effect on children’s academic and social development. Others find it hard to show that supposed negative effects are caused by the mixed aged class, while others still find that being in a mixed class has neither positive nor negative effects on the children. This essay analyses the problem by interviewing five teachers who all have a professional history where they at some point have teached mixed age classes as well as age homogenous ones. Through the use of the interviews the essay tries to contribute to the scientific understanding of mixed age classes by adding knowledge of how teachers experience the social and academic development of their pupils. To reach this purpose I start out with the following two research questions: How do teachers view the social development of their pupils in mixed age classes? How do teachers view the academic development of their pupils in mixed age classes? The results of the study show that in the teachers’ experiences, mixed age classes have a positive influence on the social development of their pupils. At the same time, however, the teachers feel that there are negative effects on the academic development, particularly within the fields of mathematics and Swedish. The result is then discussed in regards to what it may mean for Swedish schools in the short and the long run as well as if it can lead to social problems and what implications there are for what kind of people we wish to foster.