Purpose. The purpose of this study was to determine if a significant difference in the degree of teamness in high school teams whose schools have strong evidence of the five dimensions of a Professional Learning Community, compared to high school teams in schools that do not have strong evidence of the five dimensions of a Professional Learning Community. This study extended the work previously completed by Wiseman (2008) and Morr (2010). Methodology. The researcher conducted a descriptive and ex-post facto study including high school principals and their respective teachers in Riverside County, California. Two survey instruments were used to collect data. Principals were administered Huffman and Hipp's (2003) "Professional Learning Community Assessment" and teachers were assessed team characteristics by using Harvey and Drolet's (2006) "Characteristics of Effective Teams" survey. Findings. This study found that the aggregate of teacher responses resulted in a significant difference in 13 out of 17 of Harvey and Drolet's Characteristics of Effective Teams. The data also revealed that schools with strong evidence of a Professional Learning Community and schools without strong evidence of a Professional Learning Community both possessed a considerable degree of teamness. Also, Both PLC and non-PLC high schools reported high perceptions in the degree of teamness for "Clear Definition of Team Membership," "Sense of Potency/Success" and low perceptions of "Periodic Attention to Group Maintenance," "Open/Direct Conflict," and "Balanced Roles." Implications for Action. It is suggested that principals implement the PLC practices and philosophies at their schools in order to improve team effectiveness. Principals should increase professional development for assist principals and team leaders in charge of leading teams and building Professional Learning Communities. Specifically, the researcher advised principals to develop and maintain structures and processes to improve "Periodic Attention to Group Maintenance," "Open/Direct Conflict," and "Balanced Roles" as these three characteristics were ranked in the bottom three for schools with and without strong evidence of a Professional Learning Community at all levels of schools. [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.]