Background:
If school based preventive initiatives are well implemented they have the possibility to reach almost all adolescents, thereby helping to reduce the social inequality in health. However, if implementation is different according to social position, there is a risk of widening the social inequality instead.
Generally, school based smoking preventive initiatives are most effective if they target adolescent smoking from multiple sides simultaneously, i.e. structural as well as individual initiatives. However, there is a risk that especially individually oriented initiatives may be implemented different according to social position. Here we examined whether the individual level initiative of a smoking preventive intervention - a smokefree contract and dialogue - was implemented differently according to social position.

Methods:
The smoking preventive intervention - X:IT - was implemented at 51 Danish elementary schools. Main intervention components were smokefree school grounds, curricular activities, and parental involvement comprising smoke free contracts and dialogues between parents and kids.
We used questionnaire data from 2.146 pupils aged 13 years (85.0% of eligible pupils), collected after first year of intervention.

Results:
1.793 of pupils (83.6%) had signed a smokefree contract. Here 30.0% was from high, 41.7% from middle and 13.6% from low social position (14.8% was unclassifiable). Of pupils without a contract 25.0% were from high, 36.3% from middle and 16.2% from low social position (25.7% unclassifiable) (p=0.002).
1.717 pupils (80.0%) had the smokefree dialogue (high 31.2%, middle 41.9%, low 12.2%, unclassifiable 14.4%). Pupils without dialogue; high 21.0%, middle 36.6%, low 19.8%, 22.6% unclassifiable (p< .0001).

Conclusions:
The smokefree contracts and dialogues were implemented to at higher extent among kids of high social position. Parents from this social group may possess more resources to involve in school and health activities, which is an important barrier to overcome in future school based interventions.