Sustaining Professional Learning Communities
Professional learning communities may be sustained for a long period of time on the basis of essential principles of effective functioning. The suggested principles to sustain communities are; depth and breadth, stability and change, diversity and focus, and networking and integration (Louis, 2008). 
Depth and breadth
The members need to work freely on tasks over a long period of time.  Louis suggested that the members while working in collaborative teams need to be able to deal with new dilemmas, to involve new members with enthusiasm, and increase their focus on meeting arising needs. Self-assessment, support from critical friends, persistent work, and responsive adaptation should be continued. As Dufour (2004) said that complications and problems are unavoidable because those are the products of the change process. The members need to accept and address dilemmas and problems that may lead to working on tasks for a longer period of time.
Stability and change
The productivity of teams depends upon stability in team efforts and relationships. Kruse and Louis ( as cited in Louis, 2008) stated that the mobilization of the team and administrative decisions create situations where the members spend more time building trust with new members rather than focusing on work. Stable teams being cohesive may work for planning and change within the professional learning community.
Diversity and focus
Diversity and focus is another way of sustaining professional learning communities in which teams are formed by members with diverse abilities and experiences. Teams with members of alike-thinking focus more on work because trust is built easily. According to the findings of research conducted by Bolam, Stoll, and Greenwood (as cited in Louis, 2008), groups comprised of members with diverse opinions and backgrounds lead to effective problem finding and problem-solving over a period of time. The balance between groups involving diversity and role-alike groups needs to be created within a learning community.
Networking and integration
The equilibrium between the internal environment which involves the productivity of collaborative teams and the influences of the external environment which involve demands of the society is important to sustain learning communities. Bolam et al. (2005) discussed that external and internal contextual factors of a professional learning community are complex and dynamic to be controlled using both the opportunities and the limitations of a staffs’ capacities. The terms namely focus on professionalism and focus on community as used by Louis (2008) for external influences and internal productivity of teams respectively. 
Excessive professionalism is the influence of external elements such as diversity, breadth, networking, and change while community involves a focus on work, depth, integration, and stability. Excessive professionalism leads to disintegration in professional learning communities and reinforces a tradition of members as self-ruling individuals. Focus on community leads to self-satisfied teams in which challenges may not be created. Equilibrium between focusing on professionalism and focusing on the community is necessary for sustaining professional learning communities.