With the passage of the Every Student Succeeds Act (ESSA) of 2015, California state policymakers are tasked with determining the subgroup threshold for school-level reporting. To inform this decision, this policy brief explores the implications of utilizing various subgroup sizes using data from the CORE Districts. The authors find that the 20+ subgroup size presents clear advantages in terms of the number of students represented, particularly in making historically underserved student populations visible. [This memo represents work underway as part of the CORE-PACE Research Partnership. For an update to this memo, see ED574821.]