This is correct as it is in proper formatting and uses correct grammar throughout the sentence. David I disagree with you as the use of the comma in this sentence separates the two clauses, setting up the quote that follows. I work at Cornell and have seen many similar sentences and many have assumed this common mistake even though it is grammatically acceptable.
I'm afraid you are mistaken. Do you not see that the sentence is a run-on with a comma-splice error, an agreement error in the relative clause, and no period at the end? That you would assert that the sentence is free of grammar errors shows that you are difficient in your understanding of grammar.
The part of the sentence preceding the highlighted comma is a complete independent clause, and the part of the sentence following the highlighted comma is a complete independent clause. These independent clauses are not connected by a conjunction. The use of a comma leads to a run-on sentence.
As to the agreement problem within the relative clause ("that assess different children's learning styles"), the antecedent of the relative pronoun is "experiment," not "5th graders." (Fifth graders don't assess different children's learning styles; the experiment does.) "Assess" should be "assesses" (singular).
May I ask who made you a moderator?
May I ask what makes you think you have the right to disrespect me by asking such a question? If you disrespect me again, you shall be banned. Incidentally, your e-mail address has a rather foreign-sounding name, yet you have given yourself the username "William Johnson." Are you an ESL learner at Cornell?