I was reviewing the Google Classroom API and noticed there was not an option for getting grades. I need to extract the assignment grades from Google Classroom into an exter
It is possible with Google Sheets and Apps Script. You can export your grades to Google Sheets and from there, you can use Apps Script to extract data from the sheets. To do that, you can check this SO question and the methods to access and modify spreadsheet sheets.
You can definitely get grades from the API.
Classroom.Courses.CourseWork.StudentSubmissions.list(course.id, work.id).studentSubmissions
From there, loop through the studentSubmissions: studentSubmissions[i].assignedGrade
That gets the assigned grade for that specific assignment. I also grab studentSubmissions.userId in order to get the student name. Let me know if you need anything else.