The Stinson Beach Preschool will stay housed in a portable modular classroom kept on the grounds of the Bolinas-Stinson Beach Union School District for another two years, after the district approved a lease extension with the preschool during the district’s regular June board meeting. The preschool—which serves 20 families—has operated out of the modular classroom since last autumn, when it was installed by crane, said the preschool’s director, Susan Tacherra, who called the structure “a…