Найдите CSS не примененными правилами

Вы не можете использовать kwargs в атрибуте класса, потому что это аргумент ключевого слова, который был передан вашему представлению. Вы можете использовать его только в представлении.

class SubmitAttendanceView(View):
    template_name = 'schedule/submit_attendance.html'  # this html file will be included in 'schedule/scheduledetail.html'
    form_class = AttendanceForm

    def get_schedule(self, **kwargs):
        return get_object_or_404(Schedule, id=kwargs['pk'])

    def get_students(self, **kwargs):
        schedule = self.get_schedule(kwargs)
        # specify Students queryset
        students_queryset = Student.objects.filter(...)
        return students_queryset

    def get(self, request, **kwargs):
        form = self.form_class()
        students = self.get_students(kwargs)
        return render(request, self.template_name, {'form': form, 'students': students})

    def post(self, request, *args, **kwargs):
        form = self.form_class(request.POST)
        if form.is_valid():
            date = form.cleaned_data['lecture_date']
            schedule = self.get_schedule(kwargs)
            lecture = schedule.id
            subject = schedule.subject.id
            x = 1  # a counter to fetch each checkbox from template by their name
            students = self.get_students(kwargs)
            for student in self.students:
                course = Course.objects.get(id=student.course.id)
                mark = self.request.POST[f'mark{x}']
                if not mark:
                    mark = 0
                attendance = Attendance(lecture=lecture, subject=subject, course=course, student=student, lecture_date=date, mark=mark)
                attendance.save()
                x += 1
                return redirect('schedule')
        return render(request, self.template_name, {'form': form, 'students': students})