Pagination in a less hacky way...

pagination.js

// Here's the hacky way.  I'm looping 8 times, because I know I have 80 students and therefore need at least 8 pages of ten.

function getSubmissions(course, courseWork) {
  var optionalArgs = {
    pageSize: 10
  }
  var submissionObjs = [];
  for (var i=0; i<8; i++) {
    var response = Classroom.Courses.CourseWork.StudentSubmissions.list(course, courseWork, optionalArgs); // API call with necessary parameter
    optionalArgs.pageToken = response.nextPageToken; //set next page token for a new page of results on next request
    var submissions = response.studentSubmissions; // get just the array of data
    submissions.forEach(function(submission) { // loop and push each object to the result array
      submissionObjs.push(submission);
    });
  }
  return submissionObjs; // return when everything is done
}

// I tried this, but I always come up one student short...
// There may be syntax or logic errors, but I had *something* like this working to give me all but one student back.
// I would much prefer to having to manually set the loop like above!

function getSubmissions(course, courseWork) {
  var optionalArgs = {
    pageSize: 1
  }
  var submissionObjs = [];
  while (Classroom.Course.CourseWork.StudentSubmissions.list(course, courseWork, optionalArgs).pageToken) {
    var response = Classroom.Courses.CourseWork.StudentSubmissions.list(course, courseWork, optionalArgs);
    optionalArgs.pageToken = response.nextPageToken;
    submissionObjs.push(response.submissions[0]);
  }
  return submissionObj;
}