diff --git a/CHANGELOG.md b/CHANGELOG.md
index dba2ba11..7b996da7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -72,6 +72,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Maintenance
 
+- Register a `slow` pytest marker and apply it to `test_training` and `test_training_output_std` so contributors can skip long-running training tests during local iteration via `pytest -m "not slow"`. [\#651](https://github.com/mllam/neural-lam/pull/651) @sadamov
+
 - Add a short README pointer to [\#163](https://github.com/mllam/neural-lam/issues/163) for DGX Spark / PyTorch container compatibility notes, so users hitting `torch_scatter` errors know where to find the known-working / known-failing combos [\#266](https://github.com/mllam/neural-lam/pull/266) @Jayant-kernel
 
 - Group the existing Neural-LAM citation papers in the README under a `### Core Neural-LAM Publications` subheading for clearer structure [\#633](https://github.com/mllam/neural-lam/pull/633) @HetaviM29
diff --git a/pyproject.toml b/pyproject.toml
index bccec082..589c499e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -108,6 +108,11 @@ allow-any-import-level = "neural_lam"
 [tool.pylint.SIMILARITIES]
 min-similarity-lines = 10
 
+[tool.pytest.ini_options]
+markers = [
+    "slow: marks tests as slow (deselected by default, run with -m slow)",
+]
+
 [build-system]
 requires = ["hatchling>=1.27.0", "hatch-vcs"]
 build-backend = "hatchling.build"
diff --git a/tests/test_training.py b/tests/test_training.py
index 141681fc..bf1a5884 100644
--- a/tests/test_training.py
+++ b/tests/test_training.py
@@ -141,6 +141,7 @@ def run_simple_training(
     trainer.fit(model=model, datamodule=data_module)
 
 
+@pytest.mark.slow
 @pytest.mark.parametrize("datastore_name", DATASTORES.keys())
 def test_training(datastore_name):
     datastore = init_datastore_example(datastore_name)
@@ -154,6 +155,7 @@ def test_training(datastore_name):
     run_simple_training(datastore, set_output_std=False)
 
 
+@pytest.mark.slow
 def test_training_output_std():
     datastore = init_datastore_example("mdp")  # Test only with mdp datastore
     run_simple_training(datastore, set_output_std=True)