There is a widespread perception that resources of various kinds are important for the results achieved in school. Class size, teacher ratio, and teacher competence are examples of such resources. The results of research on effects of resources is, however, somewhat fragmented and unclear. This can partly be explained by uncertainties in the determination of resource variables. Making comparisons between for example authorized and unauthorized teachers has been shown to be problematic. These variables seem not to fully capture those aspects of teacher competence that are crucial for students’ performances.

This study intends to develop a precise and differentiated description of teacher competence, by focusing on both the subject-related and the pedagogical training, the type of teacher training program and to the degree of completion of the training. The meaning of the concepts authorized and unauthorized teachers thus is problematized. These newly developed categories will be important when effects of teacher competence are examined, for example when analyzing relationships between teacher qualifications and student achievements. In this study, which mainly deals with methodological problems, the categories of teacher competence will be used when analyzing variations in teacher qualifications between schools and municipalities. Longitudinal data sets with annual data collected on Swedish teachers are relied upon for these purposes.

Internationally there is vast research in this field while the Swedish research has not been extensive. Severe methodological problems have characterized this field, e.g. with respect to drawing causal conclusions from cross-sectional observational data. Some researchers (e.g. Hanushek, 1997) have concluded that there is no correlation between student achievement and various resource factors. Others (e.g. Greenwald, Hedges & Laine, 1996), however, have demonstrated a positive relationship between resources and results. Effects of resources may be mediated by other influential factors. For example, previous research (e.g. Hansson, 2012) shows that teaching organization and performance have effects on students’ mathematics achievement. Hansson also showed a between class variation in implementation of teaching, where less supportive teaching was more prevalent in classes with high needs of support, than in other classes, suggesting the existence of pedagogical segregation. A probable underlying cause may be that teacher skills are not evenly distributed among classes within the country. To analyze the significance of teacher competence, it is thus necessary both to have a valid measure and to be aware of the variation in teacher qualifications between classes, schools and municipalities.  

In recent research the factor “teacher competence” has also been demonstrated to be significant for student achievement (Gustafsson, 2003; Gustafsson & Myrberg, 2002). In line with this, Hanushek (2003) has shown a significant variation between the student outcomes that different teachers are achieving. However, the explanation of these differences needs to be further problematized and discussed. The teacher's knowledge and skills, teacher training and teaching experience are examples of factors highlighted in different meta-studies (eg, Greenwald, Hedges & Laine, 1996), that should be subject of such an investigation.

This study's aim is to implement a refined determination of the fundamental variables defining teacher competence. Two longitudinal data files are used. The change in teacher qualifications between schools and municipalities over the last twenty years is analyzed. During the same period there has been a marked increase in the proportion of unauthorized teachers in the Swedish school system. 

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