Please bring back comprehensive spaced repetition

Removing this feature and the World of Math progress circle is the biggest mistake they've made with the ongoing changes. That (and Sal's excellent explanation of concepts) was literally the only thing that made Khan Academy stand out from all the other places with math tutorials.

The lack of visual support for your (overall or topic) progress is not very motivational when it's just reduced to a tiny blue percentage under the heading. One step forward with a modern redesign, two steps back with the removal of vital features.

The following was posted by Cephalo Monk over in Content Requests and Feedback but I think it should have been posted in Feature Requests and General Site Feedback so I'm reposting it here. I totally concur with what Cephano Monk is requesting and agree that adding it would make a dramatic improvement to the site. If you want to learn more about spaced repetition, it is already employed in tools like SuperMemo and Anki. It would be amazing if Khan Academy emulated this sort of functionality!

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Hello amazing Khan Academy team members,

Firstly, thank you for all of your collective labors. I just recently broke a 414 day streak here on Khan Academy, and within that time my mathematical skills have shown marked improvement.

I did have a rather simple, but what I believe to be an empirically sound and dramatic improvement to your platform.

As you all may be aware, spaced repetition has been shown by cognitive science to be one of the best ways for retaining information over the long term. The beauty of Khan Academy is that one can easily do that on her own volition.

But, what if there was a feature, a way, one could be automatically shown/tested on those materials previously "Mastered" right before one is going to "forget" it (whenever that may fall on the forgetting curve)?

I believe this feature could be easily programmable. Specifically, let's say I successfully completed the exercises for "Multiply with Arrays" with 100% accuracy. This topic would be loaded into a "Remember System", where on the sixth or seventh day, a short 5-10 question quiz is available for one to "Refresh Your Skills".

This refresh your skills quiz would aggregate the 5-10 questions across all the topics one is about to forget. The ones which are remembered, go onto the next spaced repetition section, while those forgotten get put back into the immediate heap.

I believe this would dramatically aid in the aim of the Khan Academy goal.

Thank you all again for your efforts!