It always bugged me that during the Defense Against the Dark Arts class in their third year, every student (except for Harry and Hermione) had a boggart that took the form of something very obviously "scary." A mummy, a disembodied hand, a giant spider, etc.
"Riddikulus!" cried Parvati. A bandage unraveled at the mummy's feet; it became entangled, fell face forward, and its head rolled off.
Crack! Where the mummy had been was a woman with floorlength black hair and a skeletal, green-tinged face -- a banshee.
Crack! The banshee turned into a rat, which chased its tail in a circle, then -- crack!- became a rattlesnake, which slithered and writhed before -- crack! -- becoming a single, bloody eyeball.
Crack! The eyeball became a severed hand, which flipped over and began to creep along the floor like a crab.
Crack! Quite a few people screamed. A giant spider, six feet tall and covered in hair, was advancing on Ron, clicking its pincers menacingly.
Prisoner of Azkaban - page 113 - Bloomsbury - chapter 7, The Boggart in the Wardrobe
I understand that the kids were probably very afraid of those, but the boggart takes the form of what you most fear. Kids around 13 and 14 years old are old enough to have more abstract, deep fears than a single creature/animal.
I know that boggarts tend to become objects/people to represent a much deeper fear. Lupin's fear of his lycanthropy manifests itself as the moon. Harry's boggart is a dementor, which is "fear itself" and Hermione's boggart is later discovered to be McGonagall telling her she failed everything, which obviously represents her fear of failure. Still, the other students' fears seem overly simplistic. Ron is scared of spiders, yes, but I would think his deepest fear would have something to do with his feeling of inferiority or something.
How are these the students' "deepest fears"?