diff --git a/nbgrader/__init__.py b/nbgrader/__init__.py
index 7e68cab9..e7ecd231 100644
--- a/nbgrader/__init__.py
+++ b/nbgrader/__init__.py
@@ -3,17 +3,12 @@ A system for assigning and grading notebooks.
 """
 
 import os
+import sys
 from ._version import version_info, __version__
 
 
 def _jupyter_nbextension_paths():
-    return [
-        dict(
-            section="tree",
-            src=os.path.join('nbextensions', 'assignment_list'),
-            dest="assignment_list",
-            require="assignment_list/main"
-        ),
+    paths = [
         dict(
             section="notebook",
             src=os.path.join('nbextensions', 'create_assignment'),
@@ -34,9 +29,26 @@ def _jupyter_nbextension_paths():
         ),
     ]
 
+    if sys.platform != 'win32':
+        paths.append(
+            dict(
+                section="tree",
+                src=os.path.join('nbextensions', 'assignment_list'),
+                dest="assignment_list",
+                require="assignment_list/main"
+            )
+        )
+
+    return paths
+
+
 def _jupyter_server_extension_paths():
-    return [
-        dict(module="nbgrader.server_extensions.assignment_list"),
+    paths = [
         dict(module="nbgrader.server_extensions.formgrader"),
         dict(module="nbgrader.server_extensions.validate_assignment")
     ]
+
+    if sys.platform != 'win32':
+        paths.append(dict(module="nbgrader.server_extensions.assignment_list"))
+
+    return paths

Disable Assignment List extension on Windows
See https://github.com/conda-forge/nbgrader-feedstock/issues/12

@lgpage 
diff --git a/nbgrader/tests/apps/test_nbgrader_extension.py b/nbgrader/tests/apps/test_nbgrader_extension.py
index f0c75f3d..c636413a 100644
--- a/nbgrader/tests/apps/test_nbgrader_extension.py
+++ b/nbgrader/tests/apps/test_nbgrader_extension.py
@@ -1,25 +1,82 @@
 import os
-
 import nbgrader
+import sys
+import contextlib
+
+
+@contextlib.contextmanager
+def mock_platform(platform):
+    old_platform = sys.platform
+    sys.platform = platform
+    yield
+    sys.platform = old_platform
+
+
+def test_nbextension_linux():
+    from nbgrader import _jupyter_nbextension_paths
+    with mock_platform("linux"):
+        nbexts = _jupyter_nbextension_paths()
+        assert len(nbexts) == 4
+        assert nbexts[0]['section'] == 'notebook'
+        assert nbexts[1]['section'] == 'tree'
+        assert nbexts[2]['section'] == 'notebook'
+        assert nbexts[3]['section'] == 'tree'
+        paths = [ext['src'] for ext in nbexts]
+        for path in paths:
+            assert os.path.isdir(os.path.join(os.path.dirname(nbgrader.__file__), path))
+
+
+def test_nbextension_mac():
+    from nbgrader import _jupyter_nbextension_paths
+    with mock_platform("darwin"):
+        nbexts = _jupyter_nbextension_paths()
+        assert len(nbexts) == 4
+        assert nbexts[0]['section'] == 'notebook'
+        assert nbexts[1]['section'] == 'tree'
+        assert nbexts[2]['section'] == 'notebook'
+        assert nbexts[3]['section'] == 'tree'
+        paths = [ext['src'] for ext in nbexts]
+        for path in paths:
+            assert os.path.isdir(os.path.join(os.path.dirname(nbgrader.__file__), path))
 
 
-def test_nbextension():
+def test_nbextension_windows():
     from nbgrader import _jupyter_nbextension_paths
-    nbexts = _jupyter_nbextension_paths()
-    assert len(nbexts) == 4
-    assert nbexts[0]['section'] == 'tree'
-    assert nbexts[1]['section'] == 'notebook'
-    assert nbexts[2]['section'] == 'tree'
-    assert nbexts[3]['section'] == 'notebook'
-    paths = [ext['src'] for ext in nbexts]
-    for path in paths:
-        assert os.path.isdir(os.path.join(os.path.dirname(nbgrader.__file__), path))
-
-
-def test_serverextension():
+    with mock_platform("win32"):
+        nbexts = _jupyter_nbextension_paths()
+        assert len(nbexts) == 3
+        assert nbexts[0]['section'] == 'notebook'
+        assert nbexts[1]['section'] == 'tree'
+        assert nbexts[2]['section'] == 'notebook'
+        paths = [ext['src'] for ext in nbexts]
+        for path in paths:
+            assert os.path.isdir(os.path.join(os.path.dirname(nbgrader.__file__), path))
+
+
+def test_serverextension_linux():
+    from nbgrader import _jupyter_server_extension_paths
+    with mock_platform("linux"):
+        serverexts = _jupyter_server_extension_paths()
+        assert len(serverexts) == 3
+        assert serverexts[0]['module'] == 'nbgrader.server_extensions.formgrader'
+        assert serverexts[1]['module'] == 'nbgrader.server_extensions.validate_assignment'
+        assert serverexts[2]['module'] == 'nbgrader.server_extensions.assignment_list'
+
+
+def test_serverextension_mac():
+    from nbgrader import _jupyter_server_extension_paths
+    with mock_platform("darwin"):
+        serverexts = _jupyter_server_extension_paths()
+        assert len(serverexts) == 3
+        assert serverexts[0]['module'] == 'nbgrader.server_extensions.formgrader'
+        assert serverexts[1]['module'] == 'nbgrader.server_extensions.validate_assignment'
+        assert serverexts[2]['module'] == 'nbgrader.server_extensions.assignment_list'
+
+
+def test_serverextension_windows():
     from nbgrader import _jupyter_server_extension_paths
-    serverexts = _jupyter_server_extension_paths()
-    assert len(serverexts) == 3
-    assert serverexts[0]['module'] == 'nbgrader.server_extensions.assignment_list'
-    assert serverexts[1]['module'] == 'nbgrader.server_extensions.formgrader'
-    assert serverexts[2]['module'] == 'nbgrader.server_extensions.validate_assignment'
+    with mock_platform("win32"):
+        serverexts = _jupyter_server_extension_paths()
+        assert len(serverexts) == 2
+        assert serverexts[0]['module'] == 'nbgrader.server_extensions.formgrader'
+        assert serverexts[1]['module'] == 'nbgrader.server_extensions.validate_assignment'

pip install -e .[dev]
parse_log_pytest
requirements.txt
pyenchant sphinxcontrib-spelling sphinx_rtd_theme nbval pytest
apt-get update apt-get install -y gcc
3.5
requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
alabaster==0.7.13
alembic==1.7.7
anyio==3.6.2
argon2-cffi==21.3.0
argon2-cffi-bindings==21.2.0
async-generator==1.10
attrs==22.2.0
Babel==2.11.0
backcall==0.2.0
bleach==4.1.0
certifi==2021.5.30
cffi==1.15.1
charset-normalizer==2.0.12
comm==0.1.4
contextvars==2.4
coverage==6.2
dataclasses==0.8
decorator==5.1.1
defusedxml==0.7.1
docutils==0.18.1
entrypoints==0.4
greenlet==2.0.2
idna==3.10
imagesize==1.4.1
immutables==0.19
importlib-metadata==4.8.3
importlib-resources==5.4.0
iniconfig==1.1.1
ipykernel==5.5.6
ipython==7.16.3
ipython-genutils==0.2.0
ipywidgets==7.8.5
jedi==0.17.2
Jinja2==3.0.3
json5==0.9.16
jsonschema==3.2.0
jupyter==1.1.1
jupyter-client==7.1.2
jupyter-console==6.4.3
jupyter-core==4.9.2
jupyter-server==1.13.1
jupyterlab==3.2.9
jupyterlab-pygments==0.1.2
jupyterlab-server==2.10.3
jupyterlab_widgets==1.1.11
Mako==1.1.6
MarkupSafe==2.0.1
mistune==0.8.4
nbclassic==0.3.5
nbclient==0.5.9
nbconvert==6.0.7
nbformat==5.1.3
-e git+https://github.com/jupyter/nbgrader.git@e2f288ce4a11d08db211e67b7c0d2f9ff0c5656a#egg=nbgrader
nbval==0.10.0
nest-asyncio==1.6.0
notebook==6.4.10
packaging==21.3
pandocfilters==1.5.1
parso==0.7.1
pexpect==4.9.0
pickleshare==0.7.5
pluggy==1.0.0
prometheus-client==0.17.1
prompt-toolkit==3.0.36
ptyprocess==0.7.0
py==1.11.0
pycparser==2.21
pyenchant==3.2.2
Pygments==2.14.0
pyparsing==3.1.4
pyrsistent==0.18.0
pytest==7.0.1
python-dateutil==2.9.0.post0
pytz==2025.2
pyzmq==25.1.2
requests==2.27.1
Send2Trash==1.8.3
six==1.17.0
sniffio==1.2.0
snowballstemmer==2.2.0
Sphinx==5.3.0
sphinx-rtd-theme==2.0.0
sphinxcontrib-applehelp==1.0.2
sphinxcontrib-devhelp==1.0.2
sphinxcontrib-htmlhelp==2.0.0
sphinxcontrib-jquery==4.1
sphinxcontrib-jsmath==1.0.1
sphinxcontrib-qthelp==1.0.3
sphinxcontrib-serializinghtml==1.1.5
sphinxcontrib-spelling==7.7.0
SQLAlchemy==1.4.54
terminado==0.12.1
testpath==0.6.0
tomli==1.2.3
tornado==6.1
traitlets==4.3.3
typing_extensions==4.1.1
urllib3==1.26.20
wcwidth==0.2.13
webencodings==0.5.1
websocket-client==1.3.1
widgetsnbextension==3.6.10
zipp==3.6.0

name: nbgrader
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - pip=21.2.2=py36h06a4308_0
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - setuptools=58.0.4=py36h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - alabaster==0.7.13
      - alembic==1.7.7
      - anyio==3.6.2
      - argon2-cffi==21.3.0
      - argon2-cffi-bindings==21.2.0
      - async-generator==1.10
      - attrs==22.2.0
      - babel==2.11.0
      - backcall==0.2.0
      - bleach==4.1.0
      - cffi==1.15.1
      - charset-normalizer==2.0.12
      - comm==0.1.4
      - contextvars==2.4
      - coverage==6.2
      - dataclasses==0.8
      - decorator==5.1.1
      - defusedxml==0.7.1
      - docutils==0.18.1
      - entrypoints==0.4
      - greenlet==2.0.2
      - idna==3.10
      - imagesize==1.4.1
      - immutables==0.19
      - importlib-metadata==4.8.3
      - importlib-resources==5.4.0
      - iniconfig==1.1.1
      - ipykernel==5.5.6
      - ipython==7.16.3
      - ipython-genutils==0.2.0
      - ipywidgets==7.8.5
      - jedi==0.17.2
      - jinja2==3.0.3
      - json5==0.9.16
      - jsonschema==3.2.0
      - jupyter==1.1.1
      - jupyter-client==7.1.2
      - jupyter-console==6.4.3
      - jupyter-core==4.9.2
      - jupyter-server==1.13.1
      - jupyterlab==3.2.9
      - jupyterlab-pygments==0.1.2
      - jupyterlab-server==2.10.3
      - jupyterlab-widgets==1.1.11
      - mako==1.1.6
      - markupsafe==2.0.1
      - mistune==0.8.4
      - nbclassic==0.3.5
      - nbclient==0.5.9
      - nbconvert==6.0.7
      - nbformat==5.1.3
      - nbval==0.10.0
      - nest-asyncio==1.6.0
      - notebook==6.4.10
      - packaging==21.3
      - pandocfilters==1.5.1
      - parso==0.7.1
      - pexpect==4.9.0
      - pickleshare==0.7.5
      - pluggy==1.0.0
      - prometheus-client==0.17.1
      - prompt-toolkit==3.0.36
      - ptyprocess==0.7.0
      - py==1.11.0
      - pycparser==2.21
      - pyenchant==3.2.2
      - pygments==2.14.0
      - pyparsing==3.1.4
      - pyrsistent==0.18.0
      - pytest==7.0.1
      - python-dateutil==2.9.0.post0
      - pytz==2025.2
      - pyzmq==25.1.2
      - requests==2.27.1
      - send2trash==1.8.3
      - six==1.17.0
      - sniffio==1.2.0
      - snowballstemmer==2.2.0
      - sphinx==5.3.0
      - sphinx-rtd-theme==2.0.0
      - sphinxcontrib-applehelp==1.0.2
      - sphinxcontrib-devhelp==1.0.2
      - sphinxcontrib-htmlhelp==2.0.0
      - sphinxcontrib-jquery==4.1
      - sphinxcontrib-jsmath==1.0.1
      - sphinxcontrib-qthelp==1.0.3
      - sphinxcontrib-serializinghtml==1.1.5
      - sphinxcontrib-spelling==7.7.0
      - sqlalchemy==1.4.54
      - terminado==0.12.1
      - testpath==0.6.0
      - tomli==1.2.3
      - tornado==6.1
      - traitlets==4.3.3
      - typing-extensions==4.1.1
      - urllib3==1.26.20
      - wcwidth==0.2.13
      - webencodings==0.5.1
      - websocket-client==1.3.1
      - widgetsnbextension==3.6.10
      - zipp==3.6.0
prefix: /opt/conda/envs/nbgrader

nbgrader/tests/apps/test_nbgrader_extension.py::test_nbextension_linux nbgrader/tests/apps/test_nbgrader_extension.py::test_nbextension_mac nbgrader/tests/apps/test_nbgrader_extension.py::test_nbextension_windows nbgrader/tests/apps/test_nbgrader_extension.py::test_serverextension_linux nbgrader/tests/apps/test_nbgrader_extension.py::test_serverextension_mac nbgrader/tests/apps/test_nbgrader_extension.py::test_serverextension_windows
nbgrader/__init__.py
nbgrader/__init__.py