PurposeThis study explored implementation of the middle school concept (MSC) in Illinois middle-level schools, examining relationships between MSC implementation and schools' relative wealth, racial/ethnic composition, and achievement levels.Design/methodology/approachThis quantitative study utilized a sample of 137 Illinois middle-level schools, defined as containing any combination of grades 5–9, including at least two consecutive grade levels and grade 7. Principals completed an online survey, identifying levels of implementation of advisory, teaming with common planning time (CPT), and a composite of both advisory and teaming with CPT.FindingsSchools with high advisory implementation had significantly higher rates of Latinx enrollments. Schools with lower operating expenditures per pupil were significantly less likely to implement advisory or advisory and teaming. Teaming had a significant relationship with composite PARCC test scores, but there was no significant effect for advisory and no significant interaction of advisory and teaming together.Practical implicationsMSC is more expensive to implement, and affluent districts may have the financial means to absorb these costs. Although teaming facilitated improved state test scores, advisory programming did not result in significantly improved scores.Social implicationsLack of access to MSC programming in less affluent communities presents an equity issue for low-income students and students of color.Originality/valueThis study contributes to research examining underlying issues of race and poverty and their effects on academic achievement and the effectiveness of the MSC.