Norma Gabler, 84, a small-town Texan who wielded nationwide influence over textbook adoption in the public schools, died July 29 of complications of Parkinson’s disease at the Biltmore Assisted Living facility in Phoenix, Ariz.

She had lived in Longview, Texas, until this year, when she moved to Phoenix to be near her son.

For more than 40 years, Gabler and her husband, Mel Gabler, pored over textbook publishers’ offerings with a zeal and thoroughness that public school teachers could only envy.

Sphinx-like in their dedication and ferocity, they guarded the schoolhouse door against factual errors and what they perceived as left-wing bias. Usually one and the same in their view, the transgressions they spotted were often enough to knock the offending book from the running for statewide adoption.

Gabler and her husband, who died in 2004, exercised their outsize influence primarily because Texas public schools make up the largest textbook market in the country after California. Publishers often make their Texas offerings their national prototype.

The Gablers launched their textbook crusade in 1961 while living in Hawkins, Tex.

Their son, James Gabler, recalled that when he was assigned to recite the Gettysburg Address, he looked it up in the World Book encyclopedia and discovered two versions — a photograph of the text carved on the wall of the Lincoln Memorial and a printed version that did not include the words “under God.”

Mel Gabler recognized that the World Book in those days was as authoritative as textbooks were in public schools. He resolved to seek out errors in the books that his two sons and other Texas students were assigned to read and study. The Gablers found many. They also discovered that Texas had a little-known process for citizen textbook review, which few people used. Soon the Gablers were going to Austin to testify before the State Board of Education, wielding Texas-size clout.