Booksource Classroom uploads are compatible with Microsoft Excel 97-2003 versions. To convert a Google Sheets spreadsheet into an Excel spreadsheet that can import into Booksource Classroom, please follow the below instructions:
1) Open the Google Sheets file
2) Select 'File'
3) Select 'Download As'
4) Select .xls file type
5) Save
Once you have that .xls format, you shouldn't have any issues mass uploading students or titles into your Classroom Library.