From elsewhere on the internet
Pluto as a Planet - Until 2006, Pluto was considered the ninth planet in our solar system. However, it was reclassified as a "dwarf planet" by the International Astronomical Union due to its size and the characteristics of its orbit.
Brontosaurus as a Distinct Dinosaur - For many years, Brontosaurus was thought to be a distinct genus of dinosaur. It was later determined to be a misclassification of Apatosaurus, although more recent research has again recognized Brontosaurus as a separate genus.
The Food Pyramid - The Food Pyramid, introduced in the early 1990s, was taught as the ideal diet model. It has been criticized for its emphasis on grains at the base and has since been replaced by MyPlate in 2011, which offers a more balanced approach.
Flat Earth Theory - While not commonly taught in modern times, remnants of the Flat Earth Theory were still seriously entertained by some into the early 20th century. By 1980, it was universally accepted in education that the Earth is spherical, yet discussions of past beliefs occasionally perpetuated misinformation.
Static Universe Theory - Before the widespread acceptance of the Big Bang theory, some scientists believed the universe was static and unchanging. The discovery of cosmic microwave background radiation and the redshift of galaxies have supported the Big Bang theory, discrediting the static universe model.
Continental Drift Theory - By 1980, the theory of continental drift had evolved into the theory of plate tectonics, but earlier educational models sometimes treated continents' movements as less dynamic and complex than currently understood.
Lamarckian Evolution - Jean-Baptiste Lamarck proposed that organisms could pass on characteristics acquired during their lifetimes to their offspring. This theory has been largely debunked by modern genetics and evolutionary biology, favoring Darwin's theory of natural selection.
Racially Biased Intelligence Testing - Earlier forms of intelligence testing often contained biases that affected scoring based on race and socioeconomic status. Modern understanding of intelligence is more nuanced and recognizes these biases.
Spontaneous Generation - The idea that life can spontaneously arise from non-living matter was debunked by Louis Pasteur in the 19th century, yet snippets of this idea lingered in some educational materials into the 20th century.
The Dangers of Ulcers and Stress - It was commonly believed that stress and lifestyle factors were the primary causes of ulcers. Research in the 1980s discovered that most peptic ulcers are caused by a Helicobacter pylori infection, revolutionizing treatment and understanding of gastrointestinal health.