Table 1.

Metadata variables in the dataset.

Variable name	Description
country	Country of data collection.
waves	Participation in waves.
anonID	Anonymized individual participant's ID code.
startdate	Starting time of data collection.
month_collection	Month of data collection in each wave.
school	Anonymized ID code of participating school.
class	Anonymized ID code of participating class.
school_SES	Socio-economic status of school (varied across countries; not possible to define for Estonia and Finland).
version	Version of the questionnaire.