The importance of feedback in teaching

What is instant feedback and why is it important?
Feedback is “information provided by an agent regarding aspects of one's performance or understanding”. It’s a reaction to a learners’ action that aims to engage, inform and increase knowledge by reducing “discrepancies between current understandings and performance and a goal”.
Instant feedback is when information is provided contextually and “on-demand”, in immediate response to a learners’ action and in the flow of learning. It helps a learner deepen their understanding. After they have given input (i.e. chosen an answer) instant feedback serves to reinforce knowledge by correcting mistakes, affirming competence or debunking misconceptions on the topic. 
The more frequent and consistently you provide feedback, the better. When you follow up learning with immediate feedback, it causes learners to pause, engage, and modify behaviour in the moment. Giving feedback instantly as opposed to periodically makes learning an active rather than passive experience. 
Ideally an instant feedback loop should look like this:
As feedback is presented at a timely and relevant moment, learners can absorb or act on it then and there, while it’s contextual to present learning and top of mind. 
“[Feedback] plays a decisive role in learning and development… We learn faster, and much more effectively, when we have a clear sense of how well we are doing and what we might need in order to improve.” - Dai Hounsell, No Comment? Feedback, Learning and Development
Correcting mistakes or reinforcing answers in the flow of learning helps on three fronts - to make learning autonomous, self-directed and to better embed received information. 
When someone experiences an obstacle in learning - such as choosing an incorrect answer - and they are presented with real-time feedback about why their choice was wrong, they are motivated to set higher goals for themselves, and bridge the gap between their input and the goal, to improve performance. This satisfies a feeling of autonomy.

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They are also more likely to successfully retain the information that enabled them to progress, than if they never encountered a problem at all. In other words, providing immediate feedback enables people to better learn from any mistakes they make.
If they get the answer right to begin with, it’s still valuable to provide feedback instantly, as it reinforces why they were right. It motivates by affirming their competence. This brief moment of intervention gives context and meaning to their correct input, which makes the material more memorable. 
It’s especially important to provide real-time feedback when learning is occurring online or digitally, as there is no one present in-person to correct a mistake.