The present study evaluates the psychometric properties of the TEAM Assessment Tool. The assessment was developed to evaluate work team effectiveness as a basis for providing developmental feedback for work teams. The proposed TEAM Assessment Tool includes 12 dimensions of work team effectiveness with 90 items total. The dimension names are (a) Communication, (b) Decision-Making, (c) Performance, (d) Customer Focus, (e) Team Meetings, (f) Continuous Improvement, (g) Handling Conflict, (h) Leadership, (i) Empowerment, (j) Trust, (k) Cohesiveness/Team Relationships, and (l) Recognition and Rewards. Data were collected from employees of a large aerospace organization headquartered in the United States who are participating in work teams (N= 554). Factor analysis guided development of six new scales of team effectiveness as follows: (1) Teamwork, (2) Decision-Making, (3) Leadership Support, (4) Trust and Respect, (5) Recognition and Rewards, and (6) Customer Focus. Reliability of scales was demonstrated using Cronbach's coefficient alpha. Construct validity was demonstrated through subject matter expert (SME) input, exploratory factor analysis, and scale reliability analysis. Criterion validity was demonstrated by significant correlations at the p<.01 level comparing two measures of team member opinion of team performance and level of performance as indicated by the six subscale scores and overall scale scores of the final TEAM Assessment Tool.