When professor Brian Mittendorf asks his lecture hall full of accounting students on the first day of each semester to name the 10 highest-grossing charities in the U.S., the Red Cross, United Way or Habitat for Humanity come easily. But his students miss some big ones. “No one has ever said Fidelity Charitable or Schwab Charitable or the Silicon Valley Community Foundation,” he said of donor-advised funds. “There’s this whole other machinery playing out — just not in the public view.”