Labeling can lead to a self-fulfilling prophecy - so students are labeled as 'low-achievers' internalise that label and eventually live up to it.
FRANCIS, B., CRAIG, N., HODGEN, J., TAYLOR, B., TERESHCHENKO, CONNOLLY, P. and ARCHER, L., 2020. The impact of tracking by attainment in pupil self-confidence over time: demonstrating the accumulative impact of self-fulfilling prophecy. British Journal of Sociology of Education.14, pp 626-642.
There are more likely to be lower expectations for working-class children, this can lead to a self-fulfilling prophecy where these children become underachievers because that's all they believe they are capable of.
Teachers must ensure their practice is anti-discriminatory, and they have appropriate expectations for all pupils - regardless of social class.