In three experiments, we investigated how age-related differences in cognitive performance are exacerbated by age-based stereotype threat. We adopted a strategy approach and investigated a domain, namely arithmetic, where age-related differences in participants' performance are either non-existent or very small and where effects of age-based stereotype threat have never been investigated. In two types of tasks (problem verification in Expt. 1 and computational estimation in Expts. 2 & 3), we found that age-based stereotype threat led older adults to obtain poorer performance, to adopt less systematically and less often the better strategy on each problem, to repeat the same strategy across trials even when it was inappropriate, and to execute available strategies more poorly. We also found that poorer strategy use mediated threat effects and that individual differences in processing resources moderated individuals' sensitivity to effects of stereotype threat. Our results establish that agebased stereotype threat effects are independent of the cognitive domain or tasks in which they are studied and of pre-experimental differences in young and older adults' performance. They deepen our knowledge of the mechanisms underlying age-based, and other, stereotype threat effects. They also document how domain-general and domain-specific processing resources moderate individual differences in age-based stereotype threat effects. Our findings have important implications to improve our understanding of how and when age-based (and other) stereotype threat effects occur, and, more generally, how psychosocial factors modulate agerelated changes in human cognition.