Word for relating to class

Question

Classial? Classical? None of these are the answer. What am I supposed to say?

I want to say, "A [insert the right word here] divide," but cannot

Answer 1

Assuming that you are using "class" to refer to social status, you can, perhaps unexpectedly, just use class in your example sentence:

A class divide.

In the Boston Globe, the article "How the Travel Industry Exploits the Class Divide" makes use of this term:

The class divide is not unique to travel, Terrill said. “There’s a divide in every aspect of life,” she said. “If I go to the mall, there’s a Nieman Marcus and a Saks Fifth Avenue, and I don’t shop there. Instead I’m going to go to Macy’s and hope I can get some things on sale. So is there a divide? Yes. There’s a divide everywhere.”

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If, on the other hand, you are referring to "class" in relation to school, then your example sentence would need to be rephrased:

A class divided.
A division in the class.

Answer 2

Assuming you are referring to class as in social or economic class, the correct word is simply "class". In English we often use the phrase "a class divide".