This study investigates the effects of individual differences in working memory and different lengths of planning time on oral responses from an integrated listen-to-speak task, both in isolation and in conjunction with one another. Previous studies on planning time in a second language assessment context have largely neglected to incorporate the actual context of standardized proficiency testing where planning time is shorter than 30 seconds, leaving unanswered the question of the effects of limited planning time and its possible interaction with working memory on test taker performance and subsequently accurate construct representation. To investigate the degree to which working memory and planning time influenced oral responses, 123 Korean speakers of English completed four tasks: an integrated listen-to-speak task with a survey questionnaire, a Korean listening span task, an English listening span task, and a multiple-choice listening proficiency test. The listen-to-speak task asked the participants to listen to three short lectures and retell them in 40 seconds after 10 seconds, 20 seconds, and 60 seconds of planning time. The responses were captured by both human-awarded test scores and discourse qualities as demonstrated by complexity, accuracy, and fluency (CAF) measures. The results showed that working memory influenced neither the test scores nor the discourse qualities of oral responses in a statistically significant way, except for a minor effect on the average length of AS-units. The content scores, on the other hand, saw a significant improvement with additional planning time as little as 10 seconds. No significant interaction between working memory and planning time emerged. The study contributes to L2 assessment research on individual test taker characteristics by exploring working memory capacity as a possible source of construct-irrelevant variance in the context of integrated speaking task with limited planning time, with implications for future L2 assessment research on planning time in that the limited planning time does make a difference, along with the importance of including content-related measures as outcome to fully investigate the extent to which test taker responses vary. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]