To understand the persistent social class achievement gap, researchers have investigated how educational settings affect lower versus higher socioeconomic status (SES) students' performance. We move beyond the question of actual performance to study its assessment by evaluators. We hypothesized that even in the absence of performance differences, assessment's function of selection (i.e., compare, rank, and track students) leads evaluators to create a SES achievement gap. In 2 experiments (N ϭ 196; N ϭ 259), participants had to assess a test supposedly produced by a high-or a low-SES student, and used assessment for selection (i.e., normative grading) or learning (i.e., formative comments). Results showed that evaluators using assessment for selection found more mistakes if the test was attributed to a low-rather than a high-SES student, a difference reduced in the assessment for learning condition. The third and fourth experiments (N ϭ 374; N ϭ 306) directly manipulated the function of assessment to investigate whether the production of the social class achievement gap was facilitated by the function of selection to a greater extent than the educational function. Results of Experiment 3 supported this hypothesis. The effect did not reach significance for Experiment 4, but an internal meta-analysis confirmed that assessment used for selection led evaluators to create a SES achievement gap more than assessment used for learning, thereby contributing to the reproduction of social inequalities. Educational Impact and Implications Statement Evaluators' knowledge about students' social class can bias their assessment, in favor of privileged students. The present research suggests that assessment in itself does not trigger such a bias, nor are teachers biased in themselves; rather it is the function given to assessment that can trigger or prevent discriminatory assessment. This research found that a social class gap in evaluation appears when assessment is used for selective purposes (i.e., gauging merit and sorting students) to a greater extent that when it is used for educational purposes (i.e., fostering learning). The findings indicate that to ensure equality in educational institutions, closer attention should be paid to the role and meaning of assessment.