Well, there are poetry-writing classes, and then there’s the 1959 poetry-writing class taught by Robert Lowell at Boston University, with Sylvia Plath and Anne Sexton among the students. Kathleen Spivack was there, too, and she re-creates those heady days in her memoir, “With Robert Lowell and His Circle.” She also recalls her subsequent encounters with Elizabeth Bishop (with whom she regularly played ping-pong) and Adrienne Rich; the mentorship of Stanley Kunitz and John Malcolm Brinnin (author of the classic “Dylan Thomas in America”); her friendship with Lowell’s wives, the writers Elizabeth Hardwick and Caroline Blackwood; and the early brilliance of the critic Helen Vendler.