Grammar has long been regarded as the result of centuries of logical improvements in the systematic organization of language. Grammar has been held up as one of the defining criteria elevating mankind above mere animals.
Begun by well meaning researchers looking to improve mankind, Prescriptive Grammar and the rote drills to perfection became a practice to be ridiculed, ignored and then discarded.
In the 1920s and 1930s, two great promoters of the descriptive linguistics tradition, Edward Sapir and Leonard Bloomfield, both wrote influential books that elevated the primacy of speech over writing and the importance of a descriptive approach to language study. ....
It is interesting to note that some USA states have used 1930's Grade 6 English tests as a benchmark to show that most of the "21st century" first year college students could not even pass. Historical comparisons have revealed that education tests and standards have been deliberately reduced to disguise the failures of the "Modern public English education curriculum".
To read the original article in full: A History of English Grammar Instruction