"Half-Past Two" features anaphora in its fourth and eighth stanzas. In the first instance, the repetition of "he knew" emphasizes the depth—and limits—of the little boy's knowledge of time:
He knew a lot of time: he knew
Gettinguptime, timeyouwereofftime,
The anaphora here creates some subtle ironic humor, as it highlights the boy's confidence in his own limited knowledge: the boy is certain that he knows "a lot of time," and, from his child's perspective, he does! From an adult perspective, of course, he doesn't know much about time at all.
The phrase "he knew" appears again at the end of line 14, creating a kind of extended chiasmus:
He knew a lot of time [...] All the important times he knew,
The lines seem to fold in on themselves, creating a closed loop. This, in turn, reflects the child's simple, concise understanding of how time works.
Anaphora is even clearer in stanza 8, where it marks a major shift in the poem. By now, the little boy has now been sitting in detention for what feels like forever—since he can't tell time, he has no idea how long he's been there, or how long he's going to stay. "So he waited," says the speaker. He's patient not because he expects that his punishment will be over soon, but because he genuinely isn't sure that it will ever end. At this point, the boy "knew he'd escaped for ever"—
Into the smell of old chrysanthemums on Her desk,
Into the silent noise his hangnail made,
Into the air outside the window, into ever.
The repetition of "Into the" gives these lines (and stanza 8 as a whole) a hypnotic quality. It's almost as if the boy is falling under the power of a spell as he floats outside of the everyday experience of time.
The repetition invites the reader to become entranced, like the young boy, by everything he can smell, hear, and feel in this moment. Asyndeton adds to the effect, the lines seeming to pile up swiftly on top of one another. Nothing new is happening; instead, the poem seems to come to a standstill. But though the poem's narrative stops, the long sentence that began way back at the start of stanza 6 ("He knew the clockface [...]") continues to unfold, finally coming to a close at the end of line 24. Anaphora carries the reader towards that open-ended conclusion, "into ever." This, in turn, makes the teacher's sudden reappearance in line 25 even more surprising. After lulling the reader into a kind of trance, the poem is ready to jolt everyone "back into schooltime."