Are spaced flashcards effective for learning?
There's lots of research out there on flash cards and they are a proven, effective study aid.

Flash Cards work because of the "Forgetting Curve"; rehearsal and retrieval before you forget an item strengthens the memory before it decays allowing one to optimize encoding into LTM.



The paper Optimising learning using flashcards: Spacing is more effective than cramming is a good summary of why Spacing helps retention, highlighting why it's effective in education and should be emphasized over cramming, which current educational models (finals, tests) currently promote.

Spacing is effective for Long Term Memory as opposed to cramming/massing which is only effective (but it IS effective) in the short term as shown by the above forgetting function.