What you learned in school
Educational psychology taught that left-handedness was a defect, deficiency, or developmental problem that needed correction. Schools systematically forced left-handed children to write with their right hands, often using physical punishment or restraints. Teachers were trained to see left-handedness as abnormal behavior requiring intervention.
What we know now
Educational psychology taught that left-handedness was a defect that should be corrected. Schools forced left-handed children to write with their right hands, often using punishment to enforce this. Left-handedness was associated with clumsiness, evil, or developmental problems. Left-handedness is simply a natural variation found in about 10% of the population. Forcing children to switch hands can cause learning difficulties, speech problems, and psychological stress. Left-handed people are not abnormal or defective - they simply have different brain organization that can even confer certain advantages in some tasks.