The purpose of this study was to examine the relations of various cognitive abilities and aspects of math performance with computational estimation skill among third graders. Students (n=315) were assessed on language, nonverbal reasoning, concept formation, processing speed, long-term memory, working memory, inattentive behavior, basic reading skill, arithmetic number combination skill, double-digit computation skill, and computational estimation ability. One-way analysis of variance indicated significant differences in estimation skill among students of low, average, and high math computation performance. The unique predictors of estimation skill were arithmetic number combination skill, nonverbal reasoning, concept formation, working memory, and inattentive behavior.