diff --git a/biscuit/apps/chronos/forms.py b/biscuit/apps/chronos/forms.py
index 08a1c5c21341380e9efdf9f7938bb51f91c71125..3af258cad1ede16001cfc9b94497648bc0ee854e 100644
--- a/biscuit/apps/chronos/forms.py
+++ b/biscuit/apps/chronos/forms.py
@@ -13,7 +13,7 @@ class SelectForm(forms.Form):
         label=_('Group'), required=False)
     teacher = forms.ModelChoiceField(
         queryset=Person.objects.annotate(lessons_count=Count(
-            'lessons')).filter(lessons_count__gt=0),
+            'lessons_as_teacher')).filter(lessons_count__gt=0),
         label=_('Teacher'), required=False)
     room = forms.ModelChoiceField(
         queryset=Room.objects.annotate(lessons_count=Count(
diff --git a/biscuit/apps/chronos/model_extensions.py b/biscuit/apps/chronos/model_extensions.py
index 35afb5c3ee89649d941f8a7a8fa96ac7b2c8ba66..b4a6d4adab7ae78f62e8cbca2d0e7ee5a2da13bf 100644
--- a/biscuit/apps/chronos/model_extensions.py
+++ b/biscuit/apps/chronos/model_extensions.py
@@ -1,8 +1,18 @@
 from biscuit.core.models import Person
 
-from .models import Lesson
+from .models import Lesson, LessonPeriod
 
 
 @Person.property
 def lessons_as_participant(self):
-    return Lesson.objects.filter(groups__member=self)
+    return Lesson.objects.filter(groups__members=self)
+
+
+@Person.property
+def lesson_periods_as_participant(self):
+    return LessonPeriod.objects.filter(lesson__groups__members=self)
+
+
+@Person.property
+def lesson_periods_as_teacher(self):
+    return LessonPeriod.objects.filter(lesson__teachers=self)
diff --git a/biscuit/apps/chronos/models.py b/biscuit/apps/chronos/models.py
index 2e4e512c53949f1ff7221dfbdca61b0c17826079..675c492c1a1c0cf03795c030e7791e37b2bbc72d 100644
--- a/biscuit/apps/chronos/models.py
+++ b/biscuit/apps/chronos/models.py
@@ -10,7 +10,7 @@ from django.db.models import Q
 from django.http.request import QueryDict
 from django.utils.translation import ugettext_lazy as _
 
-from biscuit.core.mixins import SchoolRelated
+from biscuit.core.mixins import ExtensibleModel, SchoolRelated
 from biscuit.core.models import Group, Person
 
 from .util import CalendarWeek, week_weekday_from_date
@@ -274,7 +274,7 @@ class LessonSubstitution(SchoolRelated):
         ]
 
 
-class LessonPeriod(SchoolRelated):
+class LessonPeriod(SchoolRelated, ExtensibleModel):
     objects = LessonPeriodManager.from_queryset(LessonPeriodQuerySet)()
 
     lesson = models.ForeignKey('Lesson', models.CASCADE, related_name='lesson_periods')