Answer: The word in the sentence that functions as the indirect object is "class".
Explanation: An indirect object makes reference to someone or something that acts as the recipient of a direct object. In that way, the indirect object can only be present in a sentence if there is a transitive verb and a direct object. In the sentence provided, there is a transitive verb ("read") and a direct object ("the final stanza of the poem"), which receives the action of the verb; for that reason, there is also an indirect object ("class"), which makes reference to a group of people that receives the reading of that final stanza of the poem.
