Montero was promoted to High-A Palm Beach on Tuesday, Rob Rains of StLSportsPage.com reports.
The 19-year-old earned the promotion after posting very strong numbers for Low-A Peoria, hitting .321/.381/.529 with 15 homers in 102 games. Montero projects to have a decent bat with above-average raw power, though his future will depend in part on whether he can stick at third base.