The Sequoia Field Institute (tel. 559/565-3759; www.sequoiahistory.org) offers a wide variety of "Ed Ventures" spanning backpacking expeditions (about $70 a day) to writing and pottery workshops (usually about $100-$300). It also offers a "Hire a Guide" service starting at $200, where you can "rent" one of the Institute's naturalists for 4 hours.
Ranger programs include free walks and talks at Giant Forest, Lodgepole, Grant Grove, Mineral King, and Foothills. Some of the highlights include weekend wildflower walks at Foothills, talks at General Sherman, and evening campfire programs at Lodgepole. Call the park (tel. 559/565-3341) or check bulletin boards and visitor centers for the current schedule.