Alluring XXX provocateur Sheena Shaw, an athletic graduate of director John Stagliano’s “Stretch Class,” takes over as instructor, and the filmmaker’s mind- and orifice-expanding series evolves into the rough, girl-girl education of “Sheena School.” Irrepressible Sheena trains four flexible sexual adventurers in the marathon (6 hours 35 minutes) movie, implementing her own gape and gag program for advanced pupils. Sheena’s class is packed with comely, pliable ass; the scenes are long, free form sessions.