I am looking for a word or short phrase that best describes a scenario in which an author seems to have copiously placed uncommon or higher educated vocabulary in a lower reading level book. Meaning that the book seems to be for a fourth grade reading level and then every few paragraphs an English Doctorate level word appears, possibly to impress readers.
[As requested, posting this as an answer instead of a comment]
There's lexiphanic, which is using pretentious wording or language, but it doesn't have the sense of intermittence you wanted.
(I found the word by plugging "using long words" into a reverse dictionary. The first two results, sesquipedalian and sesquipedality, are also good, but they don't necessarily have a negative connotation like lexiphanic.)
I nominate erudition spikes.
Visualize a chart with the book's erudition level on the Y axis, time or position on the X axis. These sudden intrusions of sesquipedalian loquacity will appear as spikes on the graph.
the word is "Grandiloquent", if the writer has a tendency to use grand words, instead of common ones;
"Magniloquent", if the writer has a tendency to use long/large words, instead of short/small ones
Circumlocutious/circumlocutory are the words you are looking for.
M-w.com defines circumlocution (of which the above words are adjectival forms,) as :
1 : the use of an unnecessarily large number of words to express an idea 2 : evasion in speech
I would tend to use uncromulent.
ostentation - Ambitious display; pretentious parade; vain show; display intended to excite admiration or applause; A show or spectacle
sententious - excessive moralizing
That was one of J.R.R. Tolkien's strategies in writing for children. He thought that by inserting bits of higher-level phrases and vocabulary, children would learn more from reading.
So, to invent a word, I suggest using 'Tolkienesque'.
You might also consider euphuistic.
Saltation, from the Latin saltus (“to leap”) has senses including "any abrupt transition", "a light springing movement upwards or forwards", "the leaping movement of sand or soil particles [transported] over an uneven surface", "a mutation that drastically changes the phenotype of an organism or species". It might be used figuratively to indicate uneven or untoward wording: "Her vocabulary's saltation was alarming."
I'd use eccentric:
Departing from a recognized, conventional, or established norm or pattern.