Survey and tests measuring the development of the cognitive and social skills of pupils as well as the development of their social behaviour, background factors that might explain these developments in individual school careers, and influence of the school characteristics on those careers. - Pupils: Numerical skills / language skills / non-verbal intelligence / other tests CITO / well-being at school Parents: social, cultural and ethnic backgrounds of family / characteristics of pupils / characteristics of parents. Teachers : educational provision / psycho-social characteristics of pupils