I think it is very important for teachers to be emphatic on the following points:
1) We have never been visited by people from other planets.
2) Nothing of physical significance, including matter or energy or information, travels faster than the speed of light. Given the dimensions of the universe, this is a severe speed restriction.
3) We cannot move forward or backward in time.
4) You can't transport physical objects by means of radio waves.
5) There are a lot of people who would like to believe otherwise, but wishing does not equal reality.
This attitude can make a teacher a bit of a spoilsport in some contexts, but I think it's more important for the students to have the truth as a reference point as they're barraged by nominally serious claims by UFOlogists, tabloid headlines, the International Tesla Society, and some of the stranger features on The Learning Channel. And teachers: please protect your kids from pseudoscience websites. There are a lot of them, and Internet filters can't catch them.