Did I have the rights to use this Microsoft Software?

Let's say you are walking down the street one day. Some young guy dressed in shorts and a t-shirt pulls up along the curb next to you in a new BMW, jumps out, hands you the keys and says, "Here, you look like you could use a ride," before hurrying off on foot. Do you have the right to drive the car home and file a transfer of title with the DMV? Or do you assume something is wrong and the young guy did not have the right to give you the vehicle? You don't know anything about the site license, so it is hard to define whether you have could have rights. You have not mentioned if you are a substitute teacher or volunteer at the school or some similar relationship that might require you have the software to fulfill a school related duty. Or why this teacher gave you the software. Absent any legitimate explanation for why you could believe you deserve rights to the public school's software, I would assume that something is wrong and the teacher did not have the rights to give you the software.