Working-class pupils, on average, achieve less than middle-class pupils, and sociologists explain this stubborn gap in two main ways: through factors INSIDE the school (in-school or internal factors) and factors OUTSIDE it (external material and cultural factors). The view in the question prioritises in-school factors. This essay sets out the in-school case and evaluates it against the external explanations, arguing that while in-school processes are powerful and show how the gap is produced day to day, they cannot be the SOLE cause, because much disadvantage exists before the child arrives — the factors interact.
The in-school case. Interactionists locate the cause inside the school. Becker found teachers judge pupils against an image of the 'ideal pupil' that fits middle-class pupils, so working-class pupils are labelled more negatively; this label can become a self-fulfilling prophecy, demonstrated experimentally by Rosenthal and Jacobson's 'Pygmalion in the Classroom'. Ability grouping deepens this: Ball's Beachside study showed banding placed working-class pupils in lower bands with less demanding work and more negative attitudes, while Gillborn and Youdell's 'A-to-C economy' and 'educational triage' show schools concentrating resources on borderline pupils and writing others off. These processes can then push pupils into anti-school subcultures — Lacey distinguished pro-school and anti-school subcultures, and Willis's 'lads' rejected school in ways that reproduced their class position. The strength of this view is that it explains HOW underachievement is actually produced, lesson by lesson, and shows the school is not the neutral, fair sorting machine functionalists assume.
The external (material) challenge. Critics argue the deeper cause lies outside school, in material deprivation. Poor housing means no quiet study space and disturbed sleep; a lack of money means no books, computer, internet or private tuition; poorer diet and health (Howard) reduce concentration and attendance; and the 'cost of free schooling' (Bull) and the need to work further disadvantage poorer pupils. Crucially, much of this disadvantage exists BEFORE the child is ever labelled, suggesting in-school factors cannot be the whole story.
The external (cultural) challenge. Cultural explanations also locate causes in the home. Douglas stressed parental interest; Bernstein argued schools use the 'elaborated' speech code that disadvantages working-class pupils; Sugarman contrasted immediate and deferred gratification. Bourdieu's cultural capital is the strongest version: middle-class culture matches the school, advantaging middle-class pupils from the start. However, cultural deprivation theory is heavily criticised for 'blaming the victim' — Keddie argued working-class pupils are 'culturally different, not deprived'.
Evaluation. In-school factors are clearly important: labelling, grouping and subcultures demonstrably affect attainment, and they can disadvantage even materially comfortable pupils, which external explanations alone cannot capture. Yet they cannot be the MAIN cause in isolation. Material and cultural disadvantage often shape a child long before school, and in-school processes frequently RESPOND to differences pupils already bring. The most convincing position is that the factors INTERACT: a materially and culturally disadvantaged child is then labelled, set in a low band and drawn into an anti-school subculture — a chain that runs from home INTO school. Compensatory programmes such as Sure Start and Head Start try to break this chain early, but their gains often fade, showing how deep the interaction runs.
Conclusion. In-school factors are a powerful and necessary part of the explanation, because they reveal how the class gap is produced inside the classroom. But they are not the single 'main' cause: external material and cultural factors create disadvantage that the school then amplifies. The strongest explanation is therefore that internal and external factors interact, with cultural capital and in-school processes especially influential and crude 'cultural deprivation' the weakest line because it blames the victim. On balance, no single family of factors can be called the main cause — but in-school factors are best understood as the mechanism through which external disadvantage becomes educational failure.