Insights from the Early Childhood Longitudinal Study (ECLS) in the United States suggest that primary teachers who have a degree specialised in elementary education boost students’ reading performance, even compared to teachers who have more advanced degrees (Croninger et al., The effect of teachers’ qualifications is still more pronounced when aggregated at the school level: the higher the share of teachers holding advanced degrees in one school, the higher the impact on students’ performance (Croninger et al, 2007). Firstly, research finds that professional development is linked to higher quality skills among ECEC staff regardless of their educational background (Burchinal et al., Research on professional development for primary school teachers yields similar results (Angrist and Lavy, 1998, Bressoux, Kramarz and Prost, 2008).