Is it possible to turn a Sketchup file into a Sketchup for Schools and then back again?
There’s no difference. Both programs use .skp files.
Thank You I asked this because the last time i tried this it told me it wouldn’t work
Was it a file you downloaded from SketchUp for Web and tried opening in an older version of SketchUp? If that’s the case, when you download the file to your computer, you should get a prompt to choose the correct version.

No it was just download from one of my files
Next time show us the message.