A modular partition system includes a non-metallic polymer frame assembly. Horizontal members of frame sub-assemblies of the frame assembly are slidably engaged such that a width of a rectangular opening of the frame assembly can be adjusted by sliding the first frame sub-assembly and the second frame sub-assembly together or apart. Front surfaces of the frame sub-assemblies include notches on their front surfaces. The system also includes a non-metallic rectangular polymer panels with non-metallic pegs. If the width of the rectangular opening is adjusted to a specified width, the notches and the pegs align and the pegs can insert into the notches, thereby attaching the panel to the frame assembly.