I picked up an issue of Vice at the American Apparel on 29th and 7th in Manhattan. It was The Fiction Issue, and the first article I read was A TEACHER AND HER STUDENT by Thessaly La Force.
I assumed that the article was about a teacher-student affair, but it's about when Marilynne Robinson, the author of Gilead, was Thessaly's: "[...] fourth and final workshop instructor at the Iowa Writers' Workshop."
Despite the fact that Thessaly attended a prestigious writers' workshop and was a student of an author who won the Pulitzer Prize for Fiction, Thessaly confirmed my suspicion about the effectiveness of writers' workshops. She wrote:
"After receiving my MFA this May, I left Iowa believing that there's no good way to be taught how to write, to tell a story."
Thus, it appears that Jon Winokur's tweet was accurate where it was advised to writers:
"You will learn...more...from reading good literature than you will ever acquire from workshops and how-to books…”