A process for preparing a tin-containing zeolitic material having framework type BEA, comprising providing an aqueous synthesis mixture comprising a boron source, a silicon source, and a BEA structure directing agent; subjecting the synthesis mixture provided in to hydrothermal pre-crystallization conditions; adding the tin source to the obtained mixture; subjecting the obtained aqueous synthesis mixture to hydrothermal crystallization conditions, obtaining a tin-containing zeolitic material having framework type BEA comprised in its mother liquor.