No, I'm referring to spaced repetition, which is also often called spaced learning; the forgetting curve is why it works, but it is not otherwise relevant. The question about learning is how to distribute the reviews over time: all at once, or gradually over time with possibly expanding intervals. Similarly, with interleaving vs massed practice, the question is how to split up a fixed number of activities: should activity A be practiced for the maximum allowable amount of time, then B, then C and so on (analogous to massing on a single item), or should it be broken up with a few instances of A, then a few of B, and so on in a cycle until you've gone through all activities for the maximum allowable time? It turns out that for the same number of reviews or actions or exercises or time, spaced produces better recall than massed, and blocked/interleaved produces better skill learning than massed as well.