Life course models of the impact of discrimination on health and mental health outcomes posit that the pernicious effects of discrimination may not be immediate, but instead may become apparent at later stages in development. This study tests whether peer discrimination changes at particular transition points (i.e., transition to middle and high school) predict subsequent internalizing symptoms in Mexican-origin youth. In a sample of 674 Mexican-origin youth (50% female), this study used a latent change score framework to model changes in peer discrimination across time and to test whether changes in peer discrimination at 7th and 9th grades predicted greater depressive and anxiety symptoms in 12th grade controlling for 5th grade symptoms. Irrespective of longitudinal changes, greater peer discrimination in 5th grade predicted greater depressive and anxiety symptoms in 12th grade. Further, significant increases in peer discrimination from 7th to 8th grade and in 9th to 10th grade uniquely predicted greater anxiety symptoms in 12th grade. These findings suggest that longitudinal research on peer discrimination needs to take into account unique periods of risk. Future research implications are discussed.