The Principles of Adult Learning Scale (PALS) was developed and validated for measuring congruency between adult education practitioners' actual observable classroom behavior and their expressed belief in the collaborative teaching-learning mode. This model is a learner-centered instruction method in which learner and practitioner share authority for curriculum formation. A modified Likert scale is used to record responses to items which are based on the body of theory and knowledge advanced in the literature. Field research aimed to establish validity and reliability of PALS items involved the test-retest method, assessment of construct validity by a jury of adult education professors, content validity testing in public school programs, and confirmation of criterion validity by identifying the initiating and responsive actions in the items in PALS and then by comparing scores in PALS to scores on the Flanders Interaction Analysis Categories. Variables of social desirability and item interpretation congruency were also examined. PALS has potential empirical and field use. It could serve as a measurement device to segregate experimental and control groups in research studies on learning efficiency in specific teaching-learning modes. Practitioners could find uses for PALS since it consolidates many learning principles advocated in the literature. (PALS and scoring information are appended.) (CP)