Help needed for "NoReverseMatch" issue

Hello Everyone, I’m trying to develop a multi-school management system where a number of schools will be registered and each managed independently but a long the way, I got the error below, Any help is highly appreciated.

ERROR

NoReverseMatch at /en-us/schools/1/classroom/1/update/

Reverse for ‘index’ with arguments ‘(’’,)’ not found. 1 pattern(s) tried: [‘en-us/schools/(?P<school_id>\d+)/index/$’]

urls.py

url(r'^(?P<school_id>\d+)/index/$', views.index, name='index'),


url(r'^(?P<school_id>\d+)/classrooms/$', views.ClassroomListView.as_view(), name='classroom_list'),
url(r'^(?P<school_id>\d+)/classroom/create/$', views.classroom_create, name='classroom_create'),
url(r'^(?P<school_id>\d+)/classroom/(?P<classroom_id>\d+)/update/$', views.ClassroomUpdateView.as_view(),
    name='classroom_update'),

url(r'^(?P<school_id>\d+)/classroom/(?P<classroom_id>\d+)/delete/$', views.classroom_delete,
    name='classroom_delete'),

views.py

def index(request, school_id):
school = get_object_or_404(School, pk=school_id)
classroom = school.classroom_set.all()
student_count = school.student_set.count()
guardian_count = school.guardian_set.count()
employee_count = school.employee_set.count()
teacher_count = school.teacher_set.count()
context = {
‘school’: school,
‘classroom’: classroom,
‘student_count’: student_count,
‘guardian_count’: guardian_count,
‘employee_count’: employee_count,
‘teacher_count’: teacher_count,

}
return render(request, 'home/home.html', context)

class ClassroomUpdateView(UpdateView):
model = Classroom
fields = (‘classroom’, ‘numeric_name’, ‘class_teacher’, ‘note’,)
template_name = ‘classrooms/classroom_update.html’
pk_url_kwarg = ‘classroom_id’
context_object_name = ‘classroom’

def form_valid(self, form):
    classroom = form.save(commit=False)
    classroom.save()
    return redirect('classroom_list', school_id=classroom.school.pk)