The Material Safety Data Sheet (MSDS) for Elmer's washable glue states:
Chemical Product and Company Identification
DESCRIPTION: ELMER'S WASHABLE SCHOOL GLUE
PRODUCT TYPE: Chemical Product and Company Identification
Whikipedia states:
Polyvinyl acetate, PVA, PVAc, poly(ethenyl ethanoate), is a rubbery synthetic polymer with the formula (C4H6O2)n. It belongs to the polyvinyl esters family with the general formula -[RCOOCHCH2]-. It is a type of thermoplastic
So contrary to the urban legend, there is no cornstarch in Elmer's washable school glue