Using a fixed effects model, a balanced panel data set of 6,922 schools in California from 2004 to 2011 was analyzed to see whether changes in resources would affect subgroup performance at intraschool level. Seven school resources variables previously demonstrated influential to school or subgroup achievement at interschool level were tested for their effects on Academic Performance Index (API) gains of eight subgroups. Teachers’ in-district experience had the strongest positive impacts on API gains for all subgroups, ranging from 3.367 to 8.958 points, and teachers’ total experience had the largest negative impacts on subgroup API, varying between −1.120 and −5.495 points. Increases in teachers’ in-district experience, shares of highly educated and full-time equivalent teachers all offered promising outcomes for improving APIs of disadvantaged subgroups.