Two experiments examined for the first time whether the specific content of participant-generated affirmation essays—in particular, writing about social belonging—facilitated an affirmation intervention’s ability to reduce identity threat among negatively stereotyped students. Study 1, a field experiment, revealed that seventh graders assigned to a values-affirmation condition wrote about social belonging more than those assigned to a control condition. Writing about belonging, in turn, improved the grade point average (GPA) of Black, but not White students. In Study 2, using a modified “belonging-affirmation” intervention, we directly manipulated writing about social belonging before a math test described as diagnostic of math ability. The more female participants wrote about belonging, the better they performed, while there was no effect of writing about belonging for males. Writing about social belonging improved performance only for members of negatively stereotyped groups. Implications for self-affirmation theory and practice are discussed.