One critique I got of the MIT Challenge  was that I should have taken the classes over the normal four years, instead of twelve months.
The naïve version of this critique was to argue that I should do the classes the way MIT students do—full time over a period of four years.
But this criticism doesn’t hold up to scrutiny. Of course, spending more time learning something will improve how much you learn. I could have spent fifty years on those same courses and mastered them to perfection. But then I’d have spent an extra forty nine years of my life. Opportunity costs matter, whether its an extra three years or thirty.
However, some readers pointed out a more sophisticated version of the critique. This one is based on research of the spacing effect , which more or less states that the same number of hours of studying spread out over a longer interval of time results in better retention of the material.
Under this critique, I should have done the MIT Challenge over 4 years, but only spent a quarter of the time each day working on it. Quarter-time for four years instead of full-time for one.
The Spacing Effect
The spacing effect is a fairly robust observation in learning. Studies show that spreading out the same amount of practice time over multiple sessions will improve retention compared to massed practice. I recommend reading cognitive scientist Daniel Willingham’s excellent article here  for a complete summary.
Interestingly, this effect disappears when studying more complex skills. The research here is more sparse, but it seems to show that the spacing effect works better for things that need to be memorized.
To me, this seems to suggest that spacing would be a much bigger deal when studying something like languages or anatomy, which have a lot of facts to memorize, than computer science, which requires you to grok hard concepts and perform more complicated skills. Even if this is the case, however, no research I know of suggests spacing hurts retention, so it probably would still be advisable to make use of it.
If this is all true, and learning two hours a day for four years will help you retain more than eight hours per day for one, why did I run the MIT Challenge the way I did? And why run this language experiment  similarly? (Especially when remembering vocabulary words seems even more susceptible to spacing effects.)
Project Constraints and a Writer’s Compromise
The most obvious reason for my choice of a compressed one-year challenge rather than a more leisurely four, was the nature of the project itself. I wanted to see if it would be possible to learn MIT’s program well enough to pass their exams in under twelve months.
Once given those constraints, I tried to use as much spacing as possible—taking 3-4 classes in parallel, rather than sequentially. Indeed, most of the research on spacing effect is over these observed time frames, so I believe that was probably a wise move.
For my current language learning experiment, the reason is even more obvious. My current method requires immersion which isn’t something I could space out without drastic alterations.
But for my MIT Challenge, a four-year spacing could have plausibly been accomplished.
The main reason I didn’t opt for a four-year spacing is that it wouldn’t have been nearly as interesting. As a writer, that’s a compromise I’m forced to make. I’m glad the project got as many people interested in self-education as it did, so my hope is that I can offer design improvements  for those who want to do something similar, but aren’t necessarily under the constraint of writing and speaking about it.
Most the things I spend my time learning don’t form public projects. For those, I usually opt for greater spacing and a more leisurely pace.
Thoughts on Spaced Self-Education
For students in a classroom, the basic lesson of spacing is simple: don’t cram. Spread your studying time out evenly over the semester, and you’ll not only remember more for your exam, but you’ll remember more in your future classes which build off this one.
For autodidacts, I think there are some more interesting ways you can incorporate spacing into your life.
One of my favorite methods is to read blogs on the topic you’re interested in. Although blogging is less prestigious than authoring books, which may preclude some great authors from blogging, I find the format better for learning from someone’s expertise. A slow drip of ideas over a year helps digest a topic or philosophy better than reading about it in one big burst.
For skills, I think finding a way to inject regular practice into your everyday life is pivotal. When I returned from France, I made sure I always had a French book I could read to help maintain my French. Now that I’m taking on four more languages, I want to make sure I’m using all four at least once per week when I return.
My feeling is that the maintenance level of most skills is far less than the intensity required to reach a higher level. However, many people often don’t apply even that minimal amount and thus watch their skills and knowledge atrophy.
Because of this, I think the primary goal should be on finding enjoyable, interesting ways, to maintain your knowledge, not whatever system might be technically superior. Put the focus on making routines that involve the knowledge and skills you want to keep sharp.
Designing Your Learning Projects
Sometimes learning in a burst is the best way to go. Immersion with a language via travel, for example.
Generally, however, you’ll learn and retain more if you spread the same amount of time over a longer interval. This is certainly true for short intervals, such as spreading your studying over a term instead of right before an exam. But it’s likely also true for longer intervals, such as learning about a topic for years instead of all at once.
If you do have to learn in a burst, then I think the best compromise is to find a way to introduce the knowledge into your routine as a long-term habit. Small projects or weekly exposures to the topic can help ensure you won’t forget what you’ve learned.