So it isn't just about sex, it's about love and appreciation. Readers know the poet is watching because Donna's stomach is white. That is different from an Asian's skin color, and the imagery here appeals to the senses because the two cultures are lying "naked, face-up, face-down" and maybe, just maybe, he can teach her some Chinese ("Ni, wo") while the two are about to engage in physical romance.

Irony is part of the stanza in which the poet reminds his readers that while the teacher seems smart enough to bring a non-ripened persimmon to class (which the poet doesn't try to eat because he knows it isn't sweet enough), the poet knows a thing or two about persimmons. Indeed, his mom gave him really good advice by saying that persimmons have the sun inside them, "...something golden, glowing, warm as my face." He may have been punished for mispronouncing "persimmon" but the irony is he fully understands the fruit even beyond the understanding his English teacher shows.

Still more irony is to be found in the first part of the poem based on the concept and pronunciation of "precision." Okay, the poet didn't know the precise phonetic difference between "precision" and "persimmon." He messed up that part of the assignment. But wait, he does know how to be precise. He tells with exact precision how to eat the persimmon. "How to eat: put the knife away, lay down the newspaper. Peel the skin tenderly, not to tear the meat. Chew on the skin, suck it, and swallow..."

More irony is to be found in the poet's decision to part Donna's legs; he doesn't ask her if he can, he just shows the leadership of a teacher (even better than his own teacher of English who punished him) by helping her reach a physical position so the joy of sexual interaction may be wholly experienced.
Conclusion: Right after he has this moment with Donna, the poet reminds that persimmon and precision weren't the only words he had trouble with, as if telling readers that life has its good and bad. Ever the teacher, linking words to culture and life, he uses "fight" and "fright" - hence taking the opportunity to explain his childhood and juxtapose his mother with his teacher. His mom knew about persimmons, but his 6th grade teacher only knew about the pronunciation of persimmons. There's a world of difference between moms and teachers, and between people and cultures in this passage. And what made the persimmon ripe when he was in China? "The sun, the sun," he explains. In any culture, the sun makes persimmons ripe. And in any culture, there are links to other cultures that only poets know how to make beautiful and educational at the same time.