An analytical modeling to predict the bending behavior of functionally graded core sandwich beams designed with plaster and cork inclusion core and polymer skins is carried out within the framework of the present study. In addition, a microscopic analysis of the beams core using scanning electron microscope (SEM) was conducted in order to better understand the microstructural material degradation and the interaction of the cork aggregates within the plaster matrix. Accordingly, the main objective of this work is to complement the experimental observations through a theoretical prediction using high-order beam theories. In this respect, the originality of this study is to confront the modeling based on different material laws of functionally graded material (FGM)-based sandwich beams advocated in the literature to the experimental observations. Therefore, the emphasized results in terms of deflection, stiffness and stresses are compared with a good agreement to the experimental data and the advocated laws of the normalized standards. As main findings, the outcomes analysis provides a practical validated equations enabling reliable prediction of the elastic flexural response of plaster/cork FGM core sandwich beams.