APPENDIX 1.

Study sample details

	Germany	Iceland	Italy	Poland	The Netherlands	UK
Setting	Public schools, 4 school types: Gymnasium, Gemeinschaftsschule, Regional schule, Hauptschule	Public schools	Public schools, 2nd class of secondary school and 1st class of high school	Public schools, 1 school type (Gymnasium)	Public schools, 4 different school types: VMBO, HAVO, Atheneum, Gymnasium	Mainstream (state-funded) schools
Locations	Schleswig-Holstein, Germany District of Kiel, Flensburg, Schleswig-Flensburg, and Rendsburg-Eckernförde	Schools from each region (north, south, east and west) of Iceland in addition to the capital area (Reykjavík and surrounding municipalities)	Piedmont region, Italy schools with head office in Turin and Novara provinces	Wielkopolska region	Gelderland, Limburg, Brabant	Central belt of Scotland
Time of data assessment	Nov–Dec 2009	Jan–Feb 2010	March–June 2010	April–June 2010	Dec 2009–June 2010	Jan–Mar 2010
Eligibility criteria for schools	Location Number of classes >8 No special pedagogic education centre No participation in other studies of IFT-Nord	Number of participating students >100	Location in Turin and Novara provinces	Location in Wielkopolska region No special pedagogic education centre	No special pedagogic education centre No current participation in other studies of the Behavioural Science Institute, Radboud University	Location in either Midlothian or East Dumbartonshire Not providing special education Not providing private (non-state-funded) education
No. of schools potentially eligible	n=104	Not known	n=578	n=253	Not known	n=14
No. of schools invited	n=60	n=23	n=31	n=253	n=43	n=7
Invitation criteria for schools	Random	Convenience sampling	Convenience sampling	All eligible schools	Random	Selected on the basis of deprivation, based on the most recent (2007–2008) nationally available data relating to the proportion of free school meals
No. of schools that agreed to participate	n=21	n=20	n=26	n=35	n=5	N=7
Eligibility criteria for students	Active (`opt-in') parental consent Presence on the day of assessment or, if absent, willing to complete a questionnaire and return by post Willingness to participate	Passive (`opt-out') parental consent Students' presence on the day of assessment Willingness to participate	Active or passive parental consent Willingness to participate or, if absent, willing to complete a questionnaire and return by post	Active (`opt-in') parental consent Presence on the day of assessment Willingness to participate	Passive parental consent Presence on the day of assessment Willingness to participate	Passive (`opt-out') parental consent Presence on the day of assessment or, if absent, willing to complete a questionnaire and return by post Willingness to participate
No. of students examined for eligibility	n=3544	n=2798	n=2953	n=5078	n=1706	n=3189
Confirmed eligibility	n=2754	n=2662	n=2668	n=4105	n=1423	n=2937
Reasons for non-participation	No parental consent (n=515) Absence (n=264) Refusal (n=11)	No parental consent (n=19) Absence (n=104) Refusal (n=13)	No parental consent (n=100) Absence (n=175) Refusal (n=10)	No parental consent (n=396) Absence (n=527) Refusal (n=50)	No parental consent (n=18) Absence (n=265) Refusal (n=0)	No parental consent (n=11) Absence (n=226) Refusal (n=15)
Participated in the study	n=2754	n=2662	n=2668	n=4105	n=1423	n=2937
Analysed	n=2754	n=2662	n=2668	n=4105	n=1423	n=2937
Response rate	78%	95%	90%	81%	83%	92%