diff --git a/graphene/core/types/base.py b/graphene/core/types/base.py
index 8cfa603f..35f93267 100644
--- a/graphene/core/types/base.py
+++ b/graphene/core/types/base.py
@@ -5,9 +5,8 @@ import six
 
 class InstanceType(object):
 
-    @classmethod
-    def internal_type(cls, schema):
-        return getattr(cls, 'T', None)
+    def internal_type(self, schema):
+        raise NotImplementedError("internal_type for type {} is not implemented".format(self.__class__.__name__))
 
 
 class MountType(InstanceType):
diff --git a/graphene/core/types/scalars.py b/graphene/core/types/scalars.py
index d0d315b4..a87ddea2 100644
--- a/graphene/core/types/scalars.py
+++ b/graphene/core/types/scalars.py
@@ -4,21 +4,26 @@ from graphql.core.type import (GraphQLBoolean, GraphQLFloat, GraphQLID,
 from .base import MountedType
 
 
-class String(MountedType):
-    T = GraphQLString
+class ScalarType(MountedType):
+    def internal_type(self, schema):
+        return self._internal_type
 
 
-class Int(MountedType):
-    T = GraphQLInt
+class String(ScalarType):
+    _internal_type = GraphQLString
 
 
-class Boolean(MountedType):
-    T = GraphQLBoolean
+class Int(ScalarType):
+    _internal_type = GraphQLInt
 
 
-class ID(MountedType):
-    T = GraphQLID
+class Boolean(ScalarType):
+    _internal_type = GraphQLBoolean
 
 
-class Float(MountedType):
-    T = GraphQLFloat
+class ID(ScalarType):
+    _internal_type = GraphQLID
+
+
+class Float(ScalarType):
+    _internal_type = GraphQLFloat