How would I answer 'Discuss how far sociologists agree that labeling is the main reason for differences in students educational achievement.'?

Labeling - Rosenthal and Jacobson; Self -fulfilling prophecy BUT Marxists would say ...
Labeling - Rist - Tigers & Clowns BUT Feminists would say ...
Labeling - BUT The new right would say ...
Other possible factors -
Material Deprivation
Cultural Deprivation - EG. Bourdeux 'Habitus'
A combination of both; The postcode lottery - Cultural capital allows some parents to understand the schooling application system to know what to do to get their children into the best schools whilst material capital allows parents to afford houses in the catchment area of better schools or to send their children to private schools.
Conclusion - Evidence based judgments and conclusions relating to the issue of extent (how far would sociologists agree) e.g. in the judgement of the student how far does the evidence support the premise of the question