Answer

"The top" in this sentence refers to the #1 score in the class and does not refer to "among the top" scores in the class.

Manythings is an organization that lists grammatically correct sentences using certain words. http://www.manythings.org/sentences/words/top/1.html is a link I found that lists sentences with "top" in them.

It lists the sentence "Helen is always at the top of her class." This sentence is another example where "top" refers to the best.

It also lists the sentence "Tom graduated near the top of his class." this sentence is an example where "top" does not refer to the absolute best in the class. It simply refers to being among the best since he is "near the top."

Alternative sentence

http://edglossary.org/class-rank/ gives an example where it uses "top ten" and "top twenty-five percent."

So, if you would like to use a more broad version of "The work was excellent and received the top score in the class," a suitable sentence may be "The work was excellent and achieved a score among the top ten in the class." The number can be interchanged with other numbers or with a percentage such as "The work was excellent and achieved a score among the top ten percent in the class."

On top of that, you could simply say, "The work was excellent and scored among the top scores in the class." This sentence is talking about multiple scores by making scores plural instead of simply one score. This is also a suitable sentence if you would like to talk about a broader spectrum of scores.

Edit: After submitting my response, I realize that Stella Biderman already talked something similar to what I did in my previous paragraph. Therefore, I would reccomend reading her response to learn more about what I said previously.