This study investigated the effects of WML and automaticity on mental addition through an examination of both task and individual characteristics within the framework of cognitive load theory. Seventy-three fourth-grade students in New York City public schools completed the Digit Span-Backward task of the Wechsler Intelligence Scale for Children-Fifth Edition, the Math Fluency subtest of the Wechsler Individual Achievement Test-Third Edition, and a 24-item computer-assisted addition task. Results showed that working memory load, automaticity, and their interaction had significant effects on mental addition. Automaticity had a differential effect on response time under low and high WML conditions. Results also showed that working memory, math fluency, and their interaction could predict a significant portion of variance in accuracy. However, math fluency was the only significant predictor for mental addition on the measure of response time. The study confirmed the interaction effect between working memory and automaticity and underscored the importance of automaticity in arithmetic learning. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]