During the school year, cassie struggled with several subjects, including performing on math tests, to develop good work habits and studying every night.

which should be changed in the example to make the sentence parallel?

remove the coordinating conjunction.
insert an introductory clause.
make the verb tenses consistent.
the sentence is parallel.

Your answer would be that you should make the verb tenses consistent.

Explanation:

You should make the verb tenses consistent to make the sentence parallel. Parallel structure, also called parallelism, is the repetition of a chosen grammatical form within a sentence. By making each compared item follow the same grammatical pattern, you create a parallel construction. In the sentence above, including takes the VP to perform as a complement. That is why the verb takes the -ing form. Consequently, all the verbs should end in -ing (perfoming, devoloping, and studying). In this way, the sentence would have a parallel structure.

“thy baited hooks shall tangle me no more.”

“hath taught me to set in trifles no store,”

“me lusteth no longer rotten boughs to climb.”