The app had no import/export, but it turned out you could save your work in progress to a proprietary file format. I figured out the format, and then figured out how to basically take the data in google sheets and munge it into the save file format.
It took about 3 hours to enter all the grades manually, and it took about 3 hours to develop the app. So for the first time we used it, it was a wash, but then we got to use it twice more.
Sadly, then they changed report card programs and the new one used a binary file format. At least the new program allowed keyboard input with shortcuts, so it wasn't as a bad.