This study examined the overlap and validity of several measures of mother - child attachment developed for preadolescents. Validity was assessed in part by examining how attachment is related to children's mood and emotion regulation. Mother - child attachment was assessed in a sample of 9 to 11 year-old children using a story stem interview technique and questionnaires. Positive and negative mood were scored from daily logs completed by children. Emotion regulation was assessed with mothers' reports of constructive coping and teacher reports of children's ability to tolerate frustration. Interview and questionnaire measures of attachment were not consistently related to one another, although both were related to mood and emotion regulation. As expected, secure attachment and maternal secure base support were related to higher levels of positive mood, more constructive coping, and better regulation of emotion in the classroom, with effects stronger for emotion regulation than for mood. Children classified Disorganized or Ambivalent displayed the most negative mood. All effects remained significant after controlling for child temperament.