How do Holling's sentences compare to the sentences given to the other students?

The sentences that you are referring to can be found in the first chapter of Gary Schmidt's The Wednesday Wars.  

Holling's sentences are similar to the sentences that his classmates get in that they are all written in the English language and end in periods. Other than that the sentences are vastly different.  Holling's sentence is a difficult sentence to diagram because it is not a "simple" sentence. Mrs. Baker gives Holling's friends "simple" sentences that are easy to diagram. They have a single subject and a single verb.  If there is an object, it is a single object. There is no coordinating conjunction. Nothing. Holling's sentence, on the other hand, is a difficult sentence, because it strings together several independent clauses. Additionally, the vocabulary within the sentence is not something that a typical seventh grader would use.  Holling even thinks to himself the following thought:

No native speaker of the English language could diagram this sentence.  The guy who wrote it couldn't diagram this sentence.  

Here is the sentence Mrs. Baker gave to Doug.  

I read a book. 

Here is the sentence that she gave to Holling.  

For it so falls out, that what we have we prize not to the worth whiles we enjoy it; but being lacked and lost, why, then we rack the value, then we find the virtue that possession would not show us whiles it was ours.