enrollments.enrollments = $scope.selectedStudents.map(function(student) {
  return enrollments.school_class_ids.map(createEnrollments);
});

var createEnrollments = function (student) {
  return function(school_class_id) {
    return {
      enrollment: {
        registration_id: 1,
        school_class_id: school_class_id,
        status: 'active',
        unlimited: enrollments.unlimited,
        available_until: enrollments.availableUntil
      }
    }
  }
}