There is limited research examining stability and change in attachment security in middle childhood. The current study addresses this gap using data from a 3-year longitudinal study. Specifically, we examined stability and change in secure base script knowledge during middle childhood using a sample of 157 children (Wave 1 mean age [Mage] = 10.91, standard deviation [SD] = 0.87) assessed at 1-year intervals across 4 waves. Secure base script knowledge was moderately stable over time, as script scores were significantly correlated between each wave. We also investigated the impact of life stress on change in secure base script knowledge within individuals across waves. The results demonstrated that daily hassles (minor and frequently occurring stressful life events) but not major (more severe and infrequent) stressful life events predicted change in script knowledge. Implications for attachment-based interventions and, more broadly, the stability of attachment security are discussed.