Your teacher is right. However if you add a time expression at the end of it what we indicate is different. Compare;
I usually go to school at 9:00.
I am usually going to school at 9:00.
The first one tells us the action starts at 9:00.
The second one tells us the action started before 9:00 and you will be in the process of that action.
A: Can I call you at 7:00?
B: Umm I am usually (in the middle of) eating at that time so how
There is also "always" usage which means: doing something very often, too often, more than normal, which has a negative meaning. Never heard it being used without some kind of complaining actually.
I always drive to work. I do it every time.
I am always driving to work. I should ride a bike and save some money.
A few more examples;
You are always watching TV. Stop it and do something else!
My wife is always complaining. She never stops!
You are always playing video games! Go outside once in a while!