A number of nonprofit organizations and associations provide services, such as instruments, publications, and consultation, about board leadership, and presidential and leader assessment. They include:

Association of Governing Boards of Universities and Colleges (AGB)
AGB is the premier organization centered on governance in higher education, dedicated to advancing the practice of governance through advocacy, research, education, and consulting for colleges, universities, systems, and institutionally related foundations.
The mission of Boardsource is to inspire and support excellence in nonprofit governance and board and staff leadership. They offer a number of services to organizations.
Council of Independent Colleges (CIC)
CIC is an association of independent colleges and universities to support college and university leadership; advance institutional excellence; and enhance public understanding of private higher education's contribution to society.
IDEA is a nonprofit organization dedicated to improving learning in higher education through analytics, resources, and advice in many areas of interest, including leadership.
In Trust Center for Theological Schools
The In Trust Center for Theological Schools is a membership organization that strengthens the governance and institutional capacity of theological schools, promotes their health, and facilitates their renewal though Resource Consulting, education, and publications.
Board Culture Project Board Culture Board Culture Profile
Principals: Peter Eckel, Matt Hartley, and Cathy Trower provide an instrument to assess board culture.

Numerous publications about presidential leadership and assessment are available.

From my perspective, these are most relevant to our Guides.

Braskamp, Larry A. and John C. Ory. Assessing Faculty Work. San Francisco: Jossey-Bass, 1994
Braskamp, Larry A. and Jon F. Wergin. “Inside-out leadership.” Liberal Learning, AAC&U. Winter 2008.
MacTaggart, Terrence. “How Presidential Evaluations Must Change.” Trusteeship, January/February 2012.
MacTaggart, Terrence. The 21st Century Presidency: A Call to Enterprise Leadership. Washington DC: AGB Press. 2017
Morrill, Richard L. Assessing Presidential Effectiveness: A Guide for College and University Boards. Washington DC: AGB Press, 2010.
Wergin, Jon C. Administrative Leadership. IDEA Paper #56. 2014
Wheeler, Barbara G., Douglas Lewis, Sharon L. Miller, Anthony T. Ruger, and David L. Tiede. Leadership that works. Auburn Center for the Study of Theological Education, 2010.