That is correct: My mother was in school this morning.
Just in general, tense is tricky. Here are some little sentences that will help you:
Present: I eat right now.
Past: I ate yesterday.
Future: I will eat tomorrow.
Present Perfect: I have eaten many times before.
Past Perfect: I had eaten many times before.
Future Perfect: I will have eaten before you arrive.
Hope that helps!
Ms. Elaine
elaine@lessontutor.com