  Schur polynomials are special cases of Schubert polynomials, which in turn
are special cases of dual characters of flagged Weyl modules. The principal
specialization of Schur and Schubert polynomials has a long history, with
Macdonald famously expressing the principal specialization of any Schubert
polynomial in terms of reduced words. We study the principal specialization of
dual characters of flagged Weyl~modules. Our result yields an alternative proof
of a conjecture of Stanley about the principal specialization of Schubert
polynomials, originally proved by Weigandt.
