Reading aloud to Elsa and Taran (and especially Elsa now that we are able to read some chapter books) is one of the great joys of my life. Fortunately for me, I have not yet encountered any old favorites that fail to live up to my memory, although certainly some books read better than others.
By far my favorite thing about reading books aloud is that the humor comes through so much stronger. When I read humorous books to myself, I find myself thinking “oh, that was funny,” but I very rarely find myself laughing out loud. In contrast, when I’m reading to Elsa, even when she can’t possibly understand the jokes, I laugh continuously through favorites like Winnie-the-Pooh, Emily Jenkins’s Toys books, Sara Pennypacker’s Clementine books, and (of course) anything by Roald Dahl. When Elsa doesn’t get the joke, she either just laughs along with me (because it’s fun) or grills me as to why it’s funny (which is usually an intriguing experience).
Let me give you an example. This is from the first chapter of Polly Horvath’s The Trolls. The children’s parents are trying to find a babysitter:
“Well, this is a fine kettle of fish,” said Mrs. Anderson.
“What about a kennel?” said Pee Wee. “Are you going to put us in a kennel?”
“Kennels are for dogs,” said Melissa, who always knew everything.
“She said kettle,” said Amanda, who often knew everything.
“Oh,” said Pee Wee, who knew nothing and led the life of a worm.
“Who’s Sally” asked Pee Wee.
“You know Aunt Sally. We get a Christmas card from her every year. It’s a picture of a moose with tree lights strung on it.”
“Oh,” said Pee Wee. “Do you think she’ll bring her moose?”
“It’s not her moose, dummy, it’s just a funny Christmas card,” said Melissa.
“Nobody has a moose. What did you think–it was her pet or something?” said Amanda.
“A moose would make a nice pet,” said Pee Wee.
“She’s not bringing a moose,” said Melissa.
“Why do you think Daddy doesn’t want to call Aunt Sally? Wait a second, he’s picking up the phone,” said Melissa.
“Maybe he’s calling a kennel,” said Pee Wee.
“THERE WILL BE NO KENNEL!” yelled Melissa.
All this business with the moose and the kennel actually goes on through the whole first chapter, and it’s pretty funny in print, but when you start reading it to a 4-year-old with a sense of the absurd, and you’re changing voices between the children and kennels and moose are flying everywhere, you end up in tears pretty quickly.
Aside from humor, you mentioned that reading aloud calls attention to assonance and alliteration, and you are exactly right, but it is even more than that. It calls attention to the entire flow of the language. For example, take Dahl’s tongue-twistingly knotty language. I dare you to read the following passage from Matilda out loud, with the proper intonation (yelling at full volume) without having prepared it in advance:
“This clot,” boomed the Headmistress, pointing the riding-crop at him like a rapier, “this blackhead, this foul carbuncle, this poisonous pustile that you see before you is none other than a disgusting criminal, a denizen of the underworld, a member of the Mafia!”
“Who, me?” Bruce Bogtrotter said, looking genuinely puzzled.
“A thief!” the Trunchbull screamed. “A crook! A pirate! A brigand! A rustler!”
“Steady on,” the boy said. “I mean dash it all, Headmistress.”
“Do you deny it, you miserable little gumboil? Do you plead not guiltyy?”
“I don’t know what you’re talking about,” the boy said, more puzzled than ever.
“I’ll tell you what I’m talking about, you suppurating little blister!” the Trunchbull shouted. “Yesterday morning, during break, you sneaked like a serpent into the kitchen and stole a slice of my private chocolate cake from my tea-tray! That try had just been prepared for me personally by the cook! It was my morning snack! As as for the cake, it was my own private stock! That was not boy’s cake! You don’t think for one minute I’mk going to eat the filth I give to you? That cake was made from real butter and real cream! And he, that robber-bandit, that safe-cracker, that highwayman standing over there with his socks around his ankles stole it and ate it!”
Notice the staccato phrases, with no conjunctions, the bunches of hard consonants and alliteration. Aside from the fact that I was laughing so hard (especially at “stead on”) the first time I read it, it was impossible to get through. But not because Dahl is a bad writer. On the contrary–it is because he so perfectly captures Mrs. Trunchbull’s impossible personality. This is in total contrast to someone like AA Milne, whose language simply flows off your tongue and makes you want to live inside his books.
I have many more thoughts on reading aloud (including the discovery that apparently I have no fixed pronunciation for the words “aunt” and “route”), but I’ll leave it at humor and prosody for now.