@misc{Konarzewski_Krzysztof_Differentiation,
 author={Konarzewski, Krzysztof},
 howpublished={online},
 publisher={Educational Research Institute},
 language={pol},
 type={article},
 title={Differentiation of initial skills in grade 1 and birthdate effect in grade 3},
 keywords={education, school readiness, birthdate effect, PIRLS, TIMSS, HLM},
}