Robert Cass, a mathematician at Claremont McKenna College, presents a joint IAS/Princeton arithmetic geometry seminar on Schubert varieties in positive characteristic. He opens with the classical result of Mehta and Ramanathan, that Schubert varieties are Frobenius split, then turns to Bhatt's more recent proof that the full flag variety for GLn is a splinter, obtained by different methods entirely. The core of the talk is Cass's extension of Bhatt's result to all Schubert varieties for all reductive groups, work done jointly with Joao Lourenco. He shows that the same techniques carry over to affine Schubert varieties, objects that connect directly to the Langlands program and to the representation theory of algebraic groups. The talk assumes familiarity with algebraic geometry but walks through the key definitions, Frobenius splitting and the splinter property, before building toward the general theorem. It is a research-level seminar talk aimed at specialists in arithmetic and algebraic geometry.