It's an old-fashioned thing to ask, but I wouldn't assume it was differentiation, though if my 5 or 6yo child was then to recite it solo in front of an audience I might! At DS's (old fashioned, non-selective except by being fee-paying) school they did the odd bit of memorisation at age 4/5/6/7. From 8, they have Poetry Recital, at which every child stands up in turn in front of an audience of 200 or so people and, unamplified, performs a poem of 20-30 lines. I was impressed the first time, and more so by the improvement the second time. They can all do it, many of them very well.
I wouldn't be doing any kind of artificial mnemonic, except maybe at the end if there are one or two mistakes remaining; I'd just assume that lots of repetition would get it learned. I'd learn it myself and recite it together while walking anywhere, for example.
