I know IQ testing has been around for a long time but I have never understood the actual timeline. When was the first real test developed, when did it come to the US, and how long did it take for the modern version of IQ testing to emerge? I am also curious whether the tests used 100 years ago would even be recognizable compared to what a proper cognitive assessment looks like today.
The timeline is actually pretty compressed considering how much the field has developed. Alfred Binet and Theodore Simon published the first practical intelligence test in France in 1905, developed at the request of the French government to identify children needing educational support. Henry Goddard brought it to the US around 1908 and Lewis Terman at Stanford produced the Stanford Binet revision in 1916 which became the dominant American test for decades. The US military then administered mass cognitive testing to nearly two million recruits during World War One using the Army Alpha and Beta tests, which was the first large scale application of intelligence testing and dramatically accelerated public awareness of the concept. David Wechsler introduced his adult intelligence scale in 1939 which eventually became the most widely used clinical battery in the world. The modern deviation IQ replacing the original ratio formula was standardized through Wechslers work. So from Binets first test in 1905 to a recognizably modern assessment took roughly 30 to 40 years 
The World War One mass testing moment is genuinely underappreciated in the history of psychology 
Testing nearly two million people in a short period normalized the concept of cognitive assessment at a scale that would have been unimaginable just a decade earlier. It basically put IQ on the map for the general public 