diff --git a/avalanche/benchmarks/scenarios/__init__.py b/avalanche/benchmarks/scenarios/__init__.py
index f84a965c..83db8205 100644
--- a/avalanche/benchmarks/scenarios/__init__.py
+++ b/avalanche/benchmarks/scenarios/__init__.py
@@ -8,3 +8,4 @@ from .task_aware import *
 from .dataset_scenario import *
 from .exmodel_scenario import *
 from .online import *
+from .validation_scenario import *
diff --git a/avalanche/benchmarks/scenarios/dataset_scenario.py b/avalanche/benchmarks/scenarios/dataset_scenario.py
index df0848ef..cf5f7afa 100644
--- a/avalanche/benchmarks/scenarios/dataset_scenario.py
+++ b/avalanche/benchmarks/scenarios/dataset_scenario.py
@@ -14,7 +14,6 @@
 import random
 from avalanche.benchmarks.utils.data import AvalancheDataset
 import torch
-from itertools import tee
 from typing import (
     Callable,
     Generator,
@@ -253,94 +252,9 @@ class LazyTrainValSplitter:
             yield self.split_strategy(new_experience.dataset)
 
 
-def benchmark_with_validation_stream(
-    benchmark: CLScenario,
-    validation_size: Union[int, float] = 0.5,
-    shuffle: bool = False,
-    seed: Optional[int] = None,
-    split_strategy: Optional[
-        Callable[[AvalancheDataset], Tuple[AvalancheDataset, AvalancheDataset]]
-    ] = None,
-) -> CLScenario:
-    """Helper to obtain a benchmark with a validation stream.
-
-    This generator accepts an existing benchmark instance and returns a version
-    of it in which the train stream has been split into training and validation
-    streams.
-
-    Each train/validation experience will be by splitting the original training
-    experiences. Patterns selected for the validation experience will be removed
-    from the training experiences.
-
-    The default splitting strategy is a random split as implemented by `split_validation_random`.
-    If you want to use class balancing you can use `split_validation_class_balanced`, or
-    use a custom `split_strategy`, as shown in the following example::
-
-        validation_size = 0.2
-        foo = lambda exp: split_dataset_class_balanced(validation_size, exp)
-        bm = benchmark_with_validation_stream(bm, custom_split_strategy=foo)
-
-    :param benchmark: The benchmark to split.
-    :param validation_size: The size of the validation experience, as an int
-        or a float between 0 and 1. Ignored if `custom_split_strategy` is used.
-    :param shuffle: If True, patterns will be allocated to the validation
-        stream randomly. This will use the default PyTorch random number
-        generator at its current state. Defaults to False. Ignored if
-        `custom_split_strategy` is used. If False, the first instances will be
-        allocated to the training  dataset by leaving the last ones to the
-        validation dataset.
-    :param split_strategy: A function that implements a custom splitting
-        strategy. The function must accept an AvalancheDataset and return a tuple
-        containing the new train and validation dataset. By default, the splitting
-        strategy will split the data according to `validation_size` and `shuffle`).
-        A good starting to understand the mechanism is to look at the
-        implementation of the standard splitting function
-        :func:`random_validation_split_strategy`.
-
-    :return: A benchmark instance in which the validation stream has been added.
-    """
-
-    if split_strategy is None:
-        if seed is None:
-            seed = random.randint(0, 1000000)
-
-        # functools.partial is a more compact option
-        # However, MyPy does not understand what a partial is -_-
-        def random_validation_split_strategy_wrapper(data):
-            return split_validation_random(validation_size, shuffle, seed, data)
-
-        split_strategy = random_validation_split_strategy_wrapper
-    else:
-        split_strategy = split_strategy
-
-    stream = benchmark.streams["train"]
-    if isinstance(stream, EagerCLStream):  # eager split
-        train_exps, valid_exps = [], []
-
-        exp: DatasetExperience
-        for exp in stream:
-            train_data, valid_data = split_strategy(exp.dataset)
-            train_exps.append(DatasetExperience(dataset=train_data))
-            valid_exps.append(DatasetExperience(dataset=valid_data))
-    else:  # Lazy splitting (based on a generator)
-        split_generator = LazyTrainValSplitter(split_strategy, stream)
-        train_exps = (DatasetExperience(dataset=a) for a, _ in split_generator)
-        valid_exps = (DatasetExperience(dataset=b) for _, b in split_generator)
-
-    train_stream = make_stream(name="train", exps=train_exps)
-    valid_stream = make_stream(name="valid", exps=valid_exps)
-    other_streams = benchmark.streams
-
-    del other_streams["train"]
-    return CLScenario(
-        streams=[train_stream, valid_stream] + list(other_streams.values())
-    )
-
-
 __all__ = [
     "_split_dataset_by_attribute",
     "benchmark_from_datasets",
     "DatasetExperience",
     "split_validation_random",
-    "benchmark_with_validation_stream",
 ]
diff --git a/avalanche/benchmarks/scenarios/supervised.py b/avalanche/benchmarks/scenarios/supervised.py
index 66c0ecc8..8e46446d 100644
--- a/avalanche/benchmarks/scenarios/supervised.py
+++ b/avalanche/benchmarks/scenarios/supervised.py
@@ -26,12 +26,11 @@ import torch
 from avalanche.benchmarks.utils.classification_dataset import (
     ClassificationDataset,
     _as_taskaware_supervised_classification_dataset,
-    TaskAwareSupervisedClassificationDataset,
 )
 from avalanche.benchmarks.utils.data import AvalancheDataset
 from avalanche.benchmarks.utils.data_attribute import DataAttribute
 from .dataset_scenario import _split_dataset_by_attribute, DatasetExperience
-from .. import CLScenario, CLStream, EagerCLStream
+from .generic_scenario import CLScenario, CLStream, EagerCLStream
 
 
 def class_incremental_benchmark(
diff --git a/avalanche/benchmarks/scenarios/validation_scenario.py b/avalanche/benchmarks/scenarios/validation_scenario.py
new file mode 100644
index 00000000..b3cb08eb
--- /dev/null
+++ b/avalanche/benchmarks/scenarios/validation_scenario.py
@@ -0,0 +1,116 @@
+from typing import (
+    Callable,
+    Generator,
+    Generic,
+    List,
+    Sequence,
+    TypeVar,
+    Union,
+    Tuple,
+    Optional,
+    Iterable,
+    Dict,
+)
+
+import random
+from avalanche.benchmarks.utils.data import AvalancheDataset
+from .generic_scenario import EagerCLStream, CLScenario, CLExperience, make_stream
+from .dataset_scenario import (
+    LazyTrainValSplitter,
+    DatasetExperience,
+    split_validation_random,
+)
+from .supervised import with_classes_timeline
+
+
+def benchmark_with_validation_stream(
+    benchmark: CLScenario,
+    validation_size: Union[int, float] = 0.5,
+    shuffle: bool = False,
+    seed: Optional[int] = None,
+    split_strategy: Optional[
+        Callable[[AvalancheDataset], Tuple[AvalancheDataset, AvalancheDataset]]
+    ] = None,
+) -> CLScenario:
+    """Helper to obtain a benchmark with a validation stream.
+
+    This generator accepts an existing benchmark instance and returns a version
+    of it in which the train stream has been split into training and validation
+    streams.
+
+    Each train/validation experience will be by splitting the original training
+    experiences. Patterns selected for the validation experience will be removed
+    from the training experiences.
+
+    The default splitting strategy is a random split as implemented by `split_validation_random`.
+    If you want to use class balancing you can use `split_validation_class_balanced`, or
+    use a custom `split_strategy`, as shown in the following example::
+
+        validation_size = 0.2
+        foo = lambda exp: split_dataset_class_balanced(validation_size, exp)
+        bm = benchmark_with_validation_stream(bm, custom_split_strategy=foo)
+
+    :param benchmark: The benchmark to split.
+    :param validation_size: The size of the validation experience, as an int
+        or a float between 0 and 1. Ignored if `custom_split_strategy` is used.
+    :param shuffle: If True, patterns will be allocated to the validation
+        stream randomly. This will use the default PyTorch random number
+        generator at its current state. Defaults to False. Ignored if
+        `custom_split_strategy` is used. If False, the first instances will be
+        allocated to the training  dataset by leaving the last ones to the
+        validation dataset.
+    :param split_strategy: A function that implements a custom splitting
+        strategy. The function must accept an AvalancheDataset and return a tuple
+        containing the new train and validation dataset. By default, the splitting
+        strategy will split the data according to `validation_size` and `shuffle`).
+        A good starting to understand the mechanism is to look at the
+        implementation of the standard splitting function
+        :func:`random_validation_split_strategy`.
+
+    :return: A benchmark instance in which the validation stream has been added.
+    """
+
+    if split_strategy is None:
+        if seed is None:
+            seed = random.randint(0, 1000000)
+
+        # functools.partial is a more compact option
+        # However, MyPy does not understand what a partial is -_-
+        def random_validation_split_strategy_wrapper(data):
+            return split_validation_random(validation_size, shuffle, seed, data)
+
+        split_strategy = random_validation_split_strategy_wrapper
+    else:
+        split_strategy = split_strategy
+
+    stream = benchmark.streams["train"]
+    if isinstance(stream, EagerCLStream):  # eager split
+        train_exps, valid_exps = [], []
+
+        exp: DatasetExperience
+        for exp in stream:
+            train_data, valid_data = split_strategy(exp.dataset)
+            train_exps.append(DatasetExperience(dataset=train_data))
+            valid_exps.append(DatasetExperience(dataset=valid_data))
+    else:  # Lazy splitting (based on a generator)
+        split_generator = LazyTrainValSplitter(split_strategy, stream)
+        train_exps = (DatasetExperience(dataset=a) for a, _ in split_generator)
+        valid_exps = (DatasetExperience(dataset=b) for _, b in split_generator)
+
+    train_stream = make_stream(name="train", exps=train_exps)
+    valid_stream = make_stream(name="valid", exps=valid_exps)
+    other_streams = benchmark.streams
+
+    # don't drop classes-timeline for compatibility with old API
+    e0 = next(iter(train_stream))
+    if hasattr(e0, "dataset") and hasattr(e0.dataset, "targets"):
+        train_stream = with_classes_timeline(train_stream)
+        valid_stream = with_classes_timeline(valid_stream)
+
+    del other_streams["train"]
+    return CLScenario(
+        streams=[train_stream, valid_stream] + list(other_streams.values())
+    )
+
+
+__all__ = ["benchmark_with_validation_stream"]
diff --git a/avalanche/models/dynamic_modules.py b/avalanche/models/dynamic_modules.py
index 1cf58098..3086681f 100644
--- a/avalanche/models/dynamic_modules.py
+++ b/avalanche/models/dynamic_modules.py
@@ -246,7 +246,7 @@ class IncrementalClassifier(DynamicModule):
                 self.active_units[: old_act_units.shape[0]] = old_act_units
             # update with new active classes
             if self.training:
-                self.active_units[curr_classes] = 1
+                self.active_units[list(curr_classes)] = 1
 
         # update classifier weights
         if old_nclasses == new_nclasses:

diff --git a/tests/benchmarks/scenarios/test_dataset_scenario.py b/tests/benchmarks/scenarios/test_dataset_scenario.py
index d5c11eab..dbb86ab7 100644
--- a/tests/benchmarks/scenarios/test_dataset_scenario.py
+++ b/tests/benchmarks/scenarios/test_dataset_scenario.py
@@ -6,12 +6,14 @@ from torch.utils.data import TensorDataset, DataLoader
 
 from avalanche.benchmarks import (
     benchmark_from_datasets,
-    benchmark_with_validation_stream,
     CLScenario,
     CLStream,
     split_validation_random,
     task_incremental_benchmark,
 )
+from avalanche.benchmarks.scenarios.validation_scenario import (
+    benchmark_with_validation_stream,
+)
 from avalanche.benchmarks.scenarios.dataset_scenario import (
     DatasetExperience,
     split_validation_class_balanced,
@@ -383,3 +385,9 @@ class DatasetWithValidationStreamTests(unittest.TestCase):
         mb = get_mbatch(dd, len(dd))
         self.assertTrue(torch.equal(test_x, mb[0]))
         self.assertTrue(torch.equal(test_y, mb[1]))
+
+    def test_regressioni1597(args):
+        # regression test for issue #1597
+        bm = get_fast_benchmark()
+        for exp in bm.train_stream:
+            assert hasattr(exp, "classes_in_this_experience")
diff --git a/tests/training/test_plugins.py b/tests/training/test_plugins.py
index 6c223c73..9ba6dda9 100644
--- a/tests/training/test_plugins.py
+++ b/tests/training/test_plugins.py
@@ -16,6 +16,8 @@ from torch.utils.data.dataloader import DataLoader
 from avalanche.benchmarks import (
     nc_benchmark,
     GenericCLScenario,
+)
+from avalanche.benchmarks.scenarios.validation_scenario import (
     benchmark_with_validation_stream,
 )
 from avalanche.benchmarks.utils.data_loader import TaskBalancedDataLoader

benchmark_with_validation stream removes or hides classes_in_experience attribute
🐛 **Describe the bug**

When using benchmark_with_validation_stream, the classes_in_experience attribute is removed or hidden and cannot be caught during model adaptation.

🐜 **To Reproduce**

```{python}
import torch
import argparse
from torch.nn import CrossEntropyLoss
from torch.optim import SGD

from avalanche.benchmarks.classic import SplitCIFAR100
from avalanche.benchmarks import benchmark_with_validation_stream
from avalanche.models import SlimResNet18
from avalanche.models.dynamic_modules import IncrementalClassifier
from avalanche.training.supervised import Naive

def main(args):
    # Device config
    device = torch.device(
        f"cuda:{args.cuda}" if torch.cuda.is_available() and args.cuda >= 0 else "cpu"
    )

    # model
    model = SlimResNet18(1)
    model.linear = IncrementalClassifier(model.linear.in_features, model.linear.out_features)

    benchmark = SplitCIFAR100(n_experiences=5, seed=1, dataset_root="/DATA/data")
    benchmark = benchmark_with_validation_stream(benchmark, validation_size=0.05)

    # Than we can extract the parallel train and test streams
    train_stream = benchmark.train_stream
    test_stream = benchmark.test_stream

    # Prepare for training & testing
    optimizer = SGD(model.parameters(), lr=0.001, momentum=0.9)
    criterion = CrossEntropyLoss()

    # Continual learning strategy with default logger
    cl_strategy = Naive(
        model,
        optimizer,
        criterion,
        train_mb_size=32,
        train_epochs=0,
        eval_mb_size=32,
        device=device,
    )

    # train and test loop
    results = []
    for train_task in train_stream:
        print("Current Classes: ", train_task.classes_in_this_experience)
        cl_strategy.train(train_task)
        results.append(cl_strategy.eval(test_stream))


if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument(
        "--cuda",
        type=int,
        default=0,
        help="Select zero-indexed cuda device. -1 to use CPU.",
    )
    args = parser.parse_args()

    main(args)
```

🐝 **Expected behavior**

Should work with and without calling benchmark_with_validation_stream, but here gives an error

```
    print("Current Classes: ", train_task.classes_in_this_experience)
  File "/home/albin/Documents/Projects/avalanche_dev/avalanche/benchmarks/scenarios/generic_scenario.py", line 170, in __getattribute__
    v = super().__getattribute__(item)
AttributeError: 'DatasetExperience' object has no attribute 'classes_in_this_experience'
```

tests/benchmarks/scenarios/test_dataset_scenario.py::TaskIncrementalScenarioTests::test_task_incremental_bm_basic tests/benchmarks/scenarios/test_dataset_scenario.py::DatasetScenarioTests::test_benchmark_from_dataset_heterogeneous_data tests/benchmarks/scenarios/test_dataset_scenario.py::DatasetSplitterTest::test_fixed_size_experience_split_strategy tests/benchmarks/scenarios/test_dataset_scenario.py::DatasetSplitterTest::test_split_dataset_random tests/benchmarks/scenarios/test_dataset_scenario.py::DatasetWithValidationStreamTests::test_benchmark_with_validation_stream_fixed_size tests/training/test_plugins.py::EvaluationPluginTest::test_publish_metric tests/benchmarks/scenarios/test_dataset_scenario.py::DatasetWithValidationStreamTests::test_benchmark_with_validation_stream_rel_size tests/training/test_plugins.py::EvaluationPluginTest::test_forward_callbacks tests/benchmarks/scenarios/test_dataset_scenario.py::DatasetScenarioTests::test_benchmark_from_datasets tests/benchmarks/scenarios/test_dataset_scenario.py::DatasetWithValidationStreamTests::test_lazy_benchmark_with_validation_stream_fixed_size tests/training/test_plugins.py::EarlyStoppingPluginTest::test_early_stop_epochs