Can't be done. Never could. If you have a swf file that is compatible with importing into AE then it comes in as a movie.
I'm not sure what your teacher was talking about. AE files can be imported into Premiere Pro and Encore and the Adobe Media Encoder but you can't edit the original layers in anything but AE. If you import a photoshop file into Illustrator you can maintain layers but the editing isn't the same. There's no Adobe app that I know of that allows you to open a file created in one app and edit it in another app as if it were in the original app. You can use the files, but you can't manipulate them unless you go back to the original file... OOPS, one exception, some Photoshop files and some Fireworks files can be opened and edited in either app up to a point...
I see. So what do people mean when they animated a project in Adobe Flash, then composited it in Adobe After Effects?
You only create what you need in Flash or what can't be done in AE/ can be done more easily in Flash and then export only those parts. Converesely, you do stuff in AE that Flash sucks at or doesn't offer like fancy pixel-based effects. You simply have to combine the best of both worlds.