Practicing until achieving several error-free attempts is critical for retention. While this may seem like an old idea, research confirms that working many practice problems really is an important part of learning math. When learners work independently to repeatedly recall and practice (retrieval practice) new material that is beyond their current level of expertise, they become fluent in the skill and are able to recall it automatically.
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Learn how Khan Academy is designed for individual deliberate practice. Pre-assessments place students in the right level of practice, and students' avatars can change as they earn more "energy points" from problems completed correctly.