Some environmentalists are challenging Yale to put its money where its mouth is.

In a report released this week, the Sustainable Endowments Institute awarded the University a B+ in an evaluation of the 200 richest North American universities’ sustainability practices. Yale earned the same mark it did last year and trails six schools that earned an A-, including Harvard University and Dartmouth College.

Compiled by the by the nonprofit environmental advocacy group based in Cambridge, Mass., the report challenged Yale for not demonstrably matching its professed support for sustainability with financial support. The study criticized Yale for not disclosing its endowment holdings or revealing whether it invests in renewably energy and community development loan funds.

But University officials said such secrecy is vital to maintaining the $22.5 billion endowment’s impressive appreciation rate, which is crucial for further enhancing Yale’s academics, research, facilities and student life.

The second annual College Sustainability Report Card graded 129 private and 71 public universities — with combined assets totaling $343 billion — in eight categories, from food and recycling to investment priorities.

Yale netted four As and a B in the five categories related to on-campus policies and practices, earning a designation as one of 25 campus sustainability leaders. But Yale’s sagging grades in the endowment-related categories brought down its overall score and prevented it from earning the title of overall college sustainability leader, Mark Orlowski, executive director of the Sustainable Endowments Institute, said.

Julie Newman, the director of Yale’s Office of Sustainability, did not return calls seeking comment.

The grading scheme was designed to reward universities that direct their financial assets and campus policies toward promoting sustainability, Orlowski said.

“$22.5 billion carries a lot of weight, and how it’s invested and what opportunities it carries with it has a lot of impact,” he said.

Yale’s lowest grade — a D for endowment transparency — was a result of the vagueness of the University’s annual endowment report, which provides no holdings or proxy voting records, Orlowski said.

At Dartmouth, which received an A in endowment transparency and an A- overall, anyone affiliated with the university, including students and alumni, can access a listing of all publicly traded shares that the college owns directly, as well as proxy voting records, according to the report. Harvard, which publishes proxy voting records but not share holdings, received a C in endowment transparency and an A- overall.

Yale’s C in investment priorities was the lowest grade awarded in that category, Orlowski said.

“We recognize that a sizeable portion of what has to be a school’s investment priority is maximizing profit,” he said. “Dave Swensen is at the top of the game at that,” he said, referring to Yale’s chief investment officer.

Orlowski said Yale’s score could have been higher if the investments office had responded to the survey’s inquiry about whether it invested in community development loan and renewable energy funds.

Yale Law School professor Jonathan Macey, the chairman of the investment office’s advisory committee on investor responsibility, said the University does not reveal its investment portfolio as a matter of policy.

“Just like if you’re a good student, you don’t want everybody copying off your paper,” he said. “If you’re a really good portfolio manager, you don’t want everybody copying off your paper.”

Macey, who said he found Dartmouth’s holdings disclosure “astonishing,” said it would be “irresponsible” for Yale to do the same. Yale’s investment managers are concerned about other institutions’ imitating its investment strategy, he said.

Growing the endowment is key to providing the resources for improving various elements of Yale’s operations, Macey said.

“There’s a trade-off between maximizing the value of the portfolio and using the money the best we can to advance the work of the University [versus] investing in other stuff” like renewable energy, whose returns may not be as high, he said. “If we’d just gotten market returns for the past 20 years, there would be craters in the floors of colleges that are now being renovated.”

Members of the Student Taskforce for Environmental Partnership interviewed for this story expressed mixed views on the proper role of the endowment in Yale’s sustainability efforts.

STEP member Dan Bleiberg ’09 said he favors growing the endowment in order to finance more sustainable projects.

STEP coordinator John Hinkle ’09 said the investment office should strive to balance profit and principle.

“You have to strike a balance between directly sustainable investments and investments that go to making more money, because when you’re making more money you can do more with that,” he said. “But when you’re investing in things that are harmful to the environment, that’s taking a step backwards.”

Macey said his committee is charged with ensuring that Yale’s “obligation to maximize the value of the portfolio” is balanced with a strict adherence to ethical investing practices, but he said the endowment remains a target on some political agendas.

“The investment office here — because it’s such a gigantic pot of money and is so high-profile, and because of how well it has performed — appears to be a lightning rod for narrow interest groups,” he said.

Overall, a third of the schools surveyed scored a B- or better, and two-thirds improved their grade over last year.