As education became compulsory in France in the early 20th century, the Intelligence Quotient (IQ) was invented by Alfred Binet, a native psychologist, in an attempt to stratify students and to offer extra assistance to the disadvantaged. Some believed that they might benefit from interventions early in their lives so they could be spared settlement in asylums. The IQ test was composed of questions which assessed a variety of skill sets, for instance, attention, memory, and problem-solving. These were not conventionally taught at schools but were perceived to be the most accurate methods of anticipating the pupils’ achievements. According to Binet’s model, intelligence would change with age rather than remain static since birth. In addition to chronological age, he therefore introduced the principle of mental age, by which individual abilities were compared with the average scores of specific age groups. Nonetheless, he was still critical of his own testing system, which failed to take plenty of confounding variables into consideration or to address the multifactorial nature of intelligence, hence compromised generalizability.
Numerous examination tools have been developed since Binet’s endeavor. In 1916, Lewis Terman, a psychologist at Stanford University, modified Binet’s IQ test by studying a number of Americans and issued a version that corrected the original flaws and was widely recognized across the nation. The resultant Stanford-Binet IQ test has been able to spot the intellectually advanced instead of solely focusing on the lower end of the spectrum, and has further gained popularity with subsequent revisions and validations. The United States Armed Forces made use of the Army Alpha and Beta tests, which were created by another psychologist Robert Yerkes, for better appointments with regard to the capacities of the newly joined during World War I. The former was a written test, whereas the latter was devised to overcome the effects of illiteracy and language barriers. The high scorers were trained as officers while their low counterparts were discharged from the military. It was a milestone as the application of IQ measurement went beyond academic reasons.
In the middle of the last century, David Wechsler presented the novel and prominent Wechsler Adult Intelligence Scale (WAIS) to the world by making improvements to Binet’s prototype. Besides WAIS, the Wechsler Intelligence Scale for Children (WISC) and the Wechsler Preschool and Primary Scale of Intelligence (WPPSI) were specially designed for young persons. The Wechsler scales have become the most frequently used assessment tools to date and the bases on which several other testing systems have been developed.