Assignments should not be too hard or two easy, but at the right level of difficulty for the student’s level of skill or prior knowledge. The definition of the zone of proximal development (ZPD) is a bit more technical: the difference in learning that occurs with versus without a learning scaffold (e.g., tutor, teacher, text, and computer). Researchers have identified a number of zones that reflect how much learning, memory, mastery, or satisfaction occurs along a continuum of task difficulty and that is sensitive to individual differences among learners. When the material is too easy for the learner, the student is not challenged and may get bored. When it is too difficult, the student acquires very little and gets frustrated or tunes out.