diff --git a/backend/model/tribe.py b/backend/model/tribe.py
index 5833d1d..b4c5a28 100644
--- a/backend/model/tribe.py
+++ b/backend/model/tribe.py
@@ -8,6 +8,10 @@ if TYPE_CHECKING:
     from backend.model.student import Student
 
 
+class TribeError(Exception):
+    pass
+
+
 @dataclass
 class Tribe:
     name: str
@@ -18,7 +22,22 @@ class Tribe:
     def register_assessment(self, assessment: Assessment) -> None:
         self.assessments.append(assessment)
 
+    @property
+    def students_id(self) -> list[str]:
+        return [s.id for s in self.students]
+
     def register_student(self, student: Student) -> None:
+        """Register a student
+
+        If the student is already registered, it is modified.
+        """
+        try:
+            old_student = next(filter(lambda s: s.id == student.id, self.students))
+        except StopIteration:
+            pass
+        else:
+            self.students.remove(old_student)
+
         self.students.append(student)
 
     def __eq__(self, other: object) -> bool:
diff --git a/tests/model/test_student.py b/tests/model/test_student.py
index 1358d51..799e2ab 100644
--- a/tests/model/test_student.py
+++ b/tests/model/test_student.py
@@ -1,9 +1,6 @@
-from random import randint
-from uuid import UUID
-
 from backend.model.student import Student
 from backend.model.tribe import Tribe
-from tests.model.fakes import build_assessments, build_tribes
+from tests.model.fakes import build_tribes
 
 
 def test_init_student():
@@ -17,20 +14,3 @@ def test_init_student():
 
     student2 = Student(name="Hop", tribe=tribe)
     assert student.id != student2.id
-
-
-def test_tribe_register_assessment():
-    assessments_qty = randint(1, 10)
-    tribes = build_tribes(1)
-    assessments = build_assessments(tribes, assessments_qty)
-
-    assert len(tribes[0].assessments) == assessments_qty
-    assert tribes[0].assessments == assessments
-
-
-def test_tribe_register_student():
-    tribe = Tribe("foo", "2nd")
-    student = Student(id="1", name="Bob", tribe=tribe)
-
-    assert len(tribe.students) == 1
-    assert tribe.students[0] == student
diff --git a/tests/model/test_tribe.py b/tests/model/test_tribe.py
new file mode 100644
index 0000000..a26b69e
--- /dev/null
+++ b/tests/model/test_tribe.py
@@ -0,0 +1,33 @@
+from random import randint
+
+import pytest
+
+from backend.model.student import Student
+from backend.model.tribe import Tribe, TribeError
+from tests.model.fakes import build_assessments, build_tribes
+
+
+def test_tribe_register_assessment():
+    assessments_qty = randint(1, 10)
+    tribes = build_tribes(1)
+    assessments = build_assessments(tribes, assessments_qty)
+
+    assert len(tribes[0].assessments) == assessments_qty
+    assert tribes[0].assessments == assessments
+
+
+def test_tribe_register_student():
+    tribe = Tribe("foo", "2nd")
+    student = Student(id="1", name="Bob", tribe=tribe)
+
+    assert len(tribe.students) == 1
+    assert tribe.students[0] == student
+
+
+def test_tribe_register_student_already_exists_overwrite():
+    tribe = Tribe("foo", "2nd")
+    student = Student(id="1", name="Bob", tribe=tribe)
+    changed_student = Student(id="1", name="Choupy", tribe=tribe)
+
+    assert tribe.students[0] == changed_student
+    assert student.name not in [s.name for s in tribe.students]