The purpose of this study was to develop a test of academic readiness for first grade instruction in Thailand. Test of Academic Readiness (TAR) consists of six domains: verbal, visual, memory, math, logical, and general knowledge. Two pilot studies were carried out and a main study tested items in those domains. Rasch model was used to assess the scale's level of reliability and item discrimination. Content validity was claimed through extensive review of literature and similar readiness tests both in the U.S. and Thailand. TAR achieved a range of reliability between 0.73-0.93 with the exception of the visual subtest, with a reliability of 0.43. With the exception of the visual subtest, TAR has sufficient reliability to be worthwhile for future research to improve TAR as a measure of academic readiness for first grade instruction in Thailand. Further validation studies are recommended. [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/en-US/products/dissertations/individuals.shtml.]