Amy Tan is encouraged to peruse science and math over English because her vocal language may be sub par. She may have spoken with a slight Chinese accent, which in our American view, is an indication that person does not speak English well. While there is some similarities to spoken English and written English, these 2 skills are separate. A fine orator may not be the best writer.

Amy Tan is trying to disprove the thought that verbal skills indicate intelligence and writing abilities. Her mother may not speak correct English, but it does not mean she deserves poorer treatment or judgement. A child may speak "better" English, but they will still understand their mother.