  Teachable Agent (TA) is a special type of pedagogical agent which
instantiates the educational theory of Learning by Teaching. Soon after its
emergence, research of TA becomes an active field, as it can solve the over
scaffolded problem in traditional pedagogical systems, and encourage students
to take the responsibility of learning. Apart from the benefits, existing TA
design also has limitations. One is the lack of enough proactive interactions
with students during the learning process, and the other is the lack of
believability to arouse students empathy so as to offer students an immersive
learning experience. To solve these two problems, we propose a new type of TA,
Affective Teachable Agent, and use a goal oriented approach to design and
implement the agent system allowing agents to proactively interact with
students with affective expressions. The ATA model begins with the analysis of
pedagogical requirements and teaching goals, using Learning by Teaching theory
to design interventions which can authentically promote the learning behaviors
of students. Two crucial capabilities of ATA are highlighted Teachability, to
learn new knowledge and apply the knowledge to certain tasks, and
Affectivability, to establish good relationship with students and encourage
them to teach well. Through executing a hierarchy of goals, the proposed TA can
interact with students by pursuing its own agenda. When a student teaches the
agent, the agent is performed as a naive learning companion, and when an
educator teaches the agent during the design and maintenance time, the agent
can perform as an authoring tool. To facilitate the involvement of educators
into the game design, we develop an authoring tool for proposed ATA system,
which can encapsulate the technical details and provide educational experts a
natural way to convey domain knowledge to agent knowledge base.
