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The teacher's impact — when demographics are stripped away
What remains when we control for pupil background?
Everyone says the teacher matters. The difficult question is how much of school results can actually be linked to teacher certification, and how much really reflects pupils' home circumstances. By combining raw outcome measures with SALSA adjustment we get closer to an answer.
The classic correlation: certification and merit score
At school level, there is a clear positive correlation between the proportion of certified teachers and the merit score in year 9. But the spread is large. Schools with high certification can have mediocre results, and schools with lower certification can reach far higher than expected.
This does not mean the teacher is unimportant. It means that certification co-varies with pupil composition, the housing market and recruitment capacity. The chart shows why the question cannot be settled with raw merit scores alone.
Each bubble a school. The correlation is positive, but far from perfect.
Open Behörighet vs Meritvärde fullscreen →The decisive test: certification against SALSA
When we instead use SALSA deviation as the outcome measure, we filter out much of what pupils' backgrounds explain. The question then becomes sharper: do municipalities with high teacher certification also tend to perform better than expected?
The answer is yes, but cautiously. The correlation is weak rather than dramatic, which is precisely what makes it credible. Certification appears to be a real part of the explanation — but not the only one.
Municipalities with high certification land above the zero line more often, but variation remains large.
Open Lärarbehörighet vs SALSA fullscreen →Geography determines where the problem becomes acute
If certified teachers make a difference, then the regional distribution becomes critical. The map shows that access to certified teachers is highly uneven between counties. University towns and metropolitan regions generally rank higher, while much of the inland and smaller labour markets struggle significantly more.
This means the teacher question is not just about education policy but also about regional attractiveness, working conditions and municipal governance. That is why certification is one of the most concrete policy levers in the entire school debate.
Regional differences in teacher certification make educational equity a geographic question.
Open Lärarbehörighet per län fullscreen →The key finding is not that teacher certification explains everything. It does not. The key finding is that the correlation persists even when pupil background has been partly adjusted away. This makes teacher certification one of the few factors that both appears to matter and can actually be influenced politically.
For municipalities that want to improve their results, the conclusion is therefore quite concrete: attracting and retaining certified teachers is not the whole solution, but it is one of the most defensible investments they can make.