I made up a game for them to play and made a mental note to keep extra activities on hand for when my class finishes earlier than expected.

Is this correct?
My supervising teacher informed me that I speak well in class.
My supervising teacher informed me that I spoke well in class.
Which on of this sentences are correct I think it is the second on.

Your first sentence is correct.

The second two sentences are also correct.

In the first of the pair, the teacher is speaking in the present tense -- meaning that now you speak well in class. In the second of the pair, the teacher is speaking in the past tense, indicating that when he visited the class, you spoke well.

I made up a game for them to play and made a mental note to keep extra activities on hand for when my class finishes earlier than expected.

Is this correct? It'd be better to say "in case my class..." rather than "when"

My supervising teacher informed me that I speak well in class. This means that you speak well in class every time you speak.
My supervising teacher informed me that I spoke well in class. This means that you spoke well in class once, probably in the class that just ended.

Thank you

Both of the sentences have minor grammatical errors. Here are the corrected versions:

1. "I made up a game for them to play and made a mental note to keep extra activities on hand for when my class finishes earlier than expected."
Explanation: This sentence is grammatically correct. It describes that you have created a game for your class to play and have also planned to have extra activities available in case the class finishes early.

2. "My supervising teacher informed me that I speak well in class."
Explanation: This sentence is incorrect. The verb tense should be changed to match the past tense. Therefore, the correct version would be: "My supervising teacher informed me that I spoke well in class."

So, the corrected version of the second sentence would be: "My supervising teacher informed me that I spoke well in class."