**In OSF storage, you will find:** 1. The variable key and item wording for the variables used in this project (*Variable key_ St threat age daily diary_OSF.docx*) 2. The dataset containing all the variables used in this project (*Stthreat age daily diary - deidentified for OSF.sav*), except for the raw variables where participants provided qualitative information describing the stereotype threat/ stressful events. These recall variables are omitted because they are potentially identifiable. Please email the authors if you're interested in these variables 3. The R code for the analyses reported in the paper (*Stthreat daily diary_3-9-18_code for OSF.R*) **Abstract for paper** Both older and younger employees experience age-based stereotype threat in the workplace, but only older employees appear to be vulnerable to disengagement as a consequence. The present study examines two mechanisms that might explain this age difference: (1) stress appraisals of challenge and hindrance and (2) rumination. Using a weekly diary study design over five weeks, 280 employees across the lifespan (aged 18 and 66 years), completed 1,288 weekly surveys. Work outcomes examined included job satisfaction, job engagement, affective organizational commitment, workplace wellbeing, and intentions to quit. Results showed that while both older and younger employees experienced age-based stereotype threat, it was uniquely problematic for older employees. Furthermore, challenge appraisals mediated the relationships between age-based stereotype threat and job engagement, commitment, and intentions to quit among older, but not younger, employees. Rumination mediated the relationships between age-based stereotype threat and job satisfaction, commitment, wellbeing, and intentions to quit among older, but not younger, employees. These findings contribute to the literature on aging and work by shedding light on the mechanisms that link daily experiences of age-based stereotype threat with important employee outcomes.