"You are seeing the teacher" means you are dating the teacher. The verb "to see" doesn't really have a continuous form in English.
I thought that this was the course about 'formal' sentences. The translation 'you guys see the teacher' must be incorrect. I think it should be 'you (formal) see the teacher'. Am I right????
...it is 'you(formal) see the teacher. You guys see the teacher would be 'Ihr seht den Lehrer',
Because of the verb.
Sie sieht den Lehrer. = She sees the teacher.
Sie sehen den Lehrer. = You/They see the teacher.
And now to make it complicated:
Sehen Sie den Lehrer? = Do you see the teacher?
"Sie" in German can be three different things in English: "They" (plural), "She" (singular), or the polite "You" which you adress people with that are above you in hierarchy or older.
She always needs singular ending. This is not the case here. The two other forms need a plural ending, so they are an option here. But since the polite form clearly doesn't make sense it must be the third person plural they.