"The school gives too much homework," she says, as an autumn breeze blows through the open patio door of the walk-up duplex flat she rents in a Shanghai suburb to use as a home-schooling base for her son, Zhou Yi.
"Besides, he's a boy, and boys like to play, they don't like to sit still for a long time," she says, adding: "They can't just get all their knowledge from textbooks."
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Our chat is obviously distracting the boy in question, who pops up from his studies at the nearby kitchen table and goes off to fondle the family's newborn kitten and fetch his beetle collection for us to admire.
"Schools teach children in bulk, and it's not suitable for every child," Ms Cao says, adding that "each one has a different talent, and is good at different things. I don't think the rigid education in school suits my son."
Plenty of Tiger Mums and Dads around China agree with her on that one: China's education system is geared to helping millions of children each year pass the selfsame exam, the dreaded gaokao or university entrance test, widely faulted even in China for requiring too much rote learning of irrelevant content.
Many families are so desperate to avoid the gaokao that they send their children abroad to study, at an earlier and earlier age.
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But instead of sending Zhou Yi to board in Europe or the US, Ms Cao, a former fashion designer, takes him to the swimming pool at lunchtime to give him a practical lesson in the principles of flotation (which he has just finished studying in a textbook).
And every day, two hours are devoted to the study and interpretation of ancient Chinese texts. "Schools do not pay attention to traditional Chinese culture, especially the classics from Confucius and other Chinese philosophers," she says. "They are the essence of Chinese culture and as a Chinese person, my son must be familiar with them."