Learn Spanish (Latin America): ¿Tú interrumpías las clases?

Interrumpías is in the imperfect tense. We use the imperfect to talk about repeated or habitual actions in the past. In English, we often express this by saying "used to" do something. If you were asking about a single, specific time someone interrupted, you would use the preterite tense instead: ¿Interrumpiste?

Why is there an accent mark on the 'i' in interrumpías?

For regular -er and -ir verbs in the imperfect tense, every single ending starts with an accented í (-ía, -ías, -ía, -íamos, -ían). The written accent is necessary to separate the 'i' and the 'a' into two distinct syllables. Without it, your voice would blend those two vowels into a single sound.

Do I need to include the word tú in this sentence?

No, it is optional. The ending -ías is uniquely used for tú in the imperfect tense, so it is perfectly clear who you are talking about if you just ask ¿Interrumpías las clases?. Including tú here just adds a little extra emphasis to the question.

Could interrumpías also mean "were you interrupting"?