The alleged murderer was Moroccan-born but had Spanish nationality, according to Spanish diplomats in France.
Those same dipolomatic sources couldn't say whether the woman had another nationality, Spain's El País newspaper reported.
The mother, whose name was not released, attacked the teacher at the Edouard Herriot school in Albi around 9:10am, not long after the last day of school for the year had begun.
France's RTL radio said the mother tried to escape, but was detained 20 minutes later near the campus, which has some 284 pre-school and elementary students.
The mother, who was being held for questioning by police, allegedly screamed "I"m not a thief," before assaulting the teacher, Frances' BFMTV television station reported, adding the woman had previous psychiatric troubles
The mortally wounded teacher, who was stabbed in the abdomen, died around 11am, news agency AFP reported.
France's President François Hollande described the killing as a "horrific tragedy" and pledged support for children and staff at the school.
For more details see The Local France's story here.