Whenever people argue against grammar teaching it usually takes the form of the argument below.
The problem is that the “I became rich and famous without knowing X” argument can be used for almost any subject or piece of factual knowledge you like. Take maths. It’s quite possible to become rich and famous without knowing the Fibonacci sequence, stem and leaf diagrams, matrices, trigonometry, or virtually anything beyond basic arithmetic. Take English. Quite possible to become rich and famous without any knowledge of Shakespeare. Take science. I daresay Abi Elphinstone has never had to use Avogadro’s law or know chemical equations. And so it goes on with every subject you can think of.
The fact that I have never had to rotate a triangle since leaving maths class does not mean that I believe teaching children geometry is a waste of time. All knowledge is valuable and it takes knowledge to gain knowledge. Children will not know the final direction their lives will take in the future.
John Prescott became deputy prime minister with a shaky knowledge of grammar. He was unfairly mocked throughout his career because of it. Poor use of grammar does not mean low intelligence. But he doesn’t go round saying “I became wealthy and famous without much knowledge of grammar, so teaching it is a waste of time.” On the contrary, his autobiography makes it clear that he is not proud of his use of English and wishes he had been taught it in greater detail at school. Dreams and passion are all very well, but it is dangerous to suggest to children that they are all that is needed in life.