How to Make a Gold Duolingo Tree

Finishing Duolingo isn't enough; you want all the skills to be "gold," and you want them to stay gold. In this post, I'll talk about how to "regild" a completed tree, what to do about weak skills if you're half-way through a tree, and how to keep a tree gold from the very start. I'll also discuss how to do this in a way that actually teaches you something--it shouldn't be an exercise in aesthetics!

Those who are impatient can just skip straight to the end and read what I recommend as the best practice. For everyone else, I'll explain what it is we're talking about and how I reached the conclusions I did.

The Decaying Tree

When you first finish a skill, Duolingo turns its icon gold, and five "strength bars" (like on your phone) appear beside it. If you don't do regular "strengthening" exercises, though, the strength bars will gradually weaken from five to one, and at anything less than five, the skill appears in its original color--not gold. This is what we mean by "strong skills" and "weak skills." "Regilding the tree" means doing enough exercises to turn the whole tree gold again.

People who do new lessons but never do review lessons get used to the way a wave of color chases them down their tree. Those who took the placement test and skipped over a large part of the tree are often stunned when a huge slab abruptly turns color all at once. In both cases, Duolingo is sending a message that those are skills that ought to be reviewed. This post is for those who want to do something about weak skills and who want to enhance their language learning at the same time.

Why Bother?

As Duolingo warns, if you don't review what you learned, you'll start to forget it. Lots of people eventually abandon Duolingo because they get about a third of the way down the tree and then they have terrible trouble finishing new lessons, due to the fact that they've forgotten too much of the earlier material. Doing regular review lessons spares you from this.

Duolingo has a decent algorithm that tries to target the things you most need to review. Done right, the review lessons really shouldn't end up being a waste of time--they should help you solidify your understanding of the language. And they often contain material you didn't see when you did the skill for the first time.

Two Kind of Strengthening Exercises

To reverse this decay process, you can either do a skill-specific strengthening exercise or a general strengthening exercise. To do a skill-specific one, you pick a weakened skill and click on its icon. On the right, you'll see a colored box showing the strength of the skill, and inside that box is a button to strengthen the skill. Press that button and Duolingo gives you a review lesson targeting the skill as a whole. That is, it doesn't just repeat one of the lessons--it asks you questions drawn from all of them.

Because it only takes 17 correct answers to complete a lesson, and because Duolingo usually has far more than 17 possible questions per lesson, when you do a review lesson you will frequently see sentences you never saw when you did the skill in the first place. Usually not entirely new words, but you'll definitely see new ways to use the old words.

Depending on how weak the skill is and how big it is (i.e. how many words it covers), a single strengthening exercise may not be enough to make it gold again. Repetition may be necessary. On the other hand, occasionally you'll strengthen some entirely different skill that just happens to share a few words with the one you were trying to strengthen.

To do a general strengthening exercise, you go back to the main menu and click the blue "Strengthen Skills" button on the far right of the screen." This brings up a review lesson that has a random mix of things you have already studied but that Duolingo thinks are weakest.

Because the benefits of the general exercise are spread across the entire tree, it usually strengthens anywhere from zero to three skills--some people have reported as many as 13.

In short, your tree weakens over time, and you have to do strengthening exercises if you want it to stay (or become) gold. The question is how often to do them and what kind to do. To answer that, we'll start with a look at Duolingo's algorithm--what's known of it, anyway.

How it Works

Duolingo does not publish much about the algorithms they use for weakening and strengthening, but they did make at least one posting with hints about it. Further, a Duolingo user with the handle pinkodoug has made an extensive study of the Duolingo JavaScript and he has some plausible ideas about their algorithms for strengthening and weakening.

Drawing from those sources plus my own experiments, here's my best guess as to what they do. (N.B. these are my conclusions, so if they're wrong blame me--not the sources above.)

To Duolingo, strength is about words, not skills. Strong words have a score of 100%, and they decay over time until they reach zero. All words are decaying all the time, but some words decay faster than others.

You can actually see this if you click on the "Words" tab at the top of the home screen.

This shows all the words that Duolingo thinks you've studied so far. It tells you how long ago you practiced each one, and it gives each word's current strength using a bar system that goes from 1-4 (not 1-5 the way skills do). If you sort by "Last Practiced," you'll see that the older words tend to be weak while the latest words are almost all 4-bars strong. This is because all words weaken over time, but, as I said before, some words decay faster than others. We'll get back to this last point in a minute.

Every skill is associated with a set of words--probably the same words that you see in the individual lesson descriptions. Whenever those words have an average strength of 2.5 bars or more, the skill is gold. Otherwise, it shows the original color, and the skill-strength declines based on some function of the average word strength.

Whenever you do a review lesson, it targets some number of your weakest words for review. A skill-specific review only picks words from that one skill. A general review picks words from every lesson you've completed so far. Otherwise they're the same--with one important exception: in the tips that Duolingo offered, they said that skill-specific strengthening turns your tree gold faster than general strengthening does.

As long as you complete the review lesson, the targeted words all get set back to four bars whether you get them right or not. The catch is that getting them right makes them decay slower in the future. Getting them wrong or using the hints makes them decay faster. This is why some people report making tremendous efforts to strengthen every single skill only to watch them start decaying again a few days later.

The fact that some people seem to keep their trees gold without much effort suggests that there actually is an optimal way to do this. To determine what that might be, I did a few experiments--with help from a friend.

Experiments

Greg's French Tree

For the past twelve months, I have been slowly going through Duolingo's French tree, following a rule of doing two review lessons per day followed by one new lesson. In that time, I have completed most of the tree, and it has never weakened. That is, although an individual skill has weakened two or three times, I simply strengthened it specifically and thus ended the day with a solid-gold tree. During that time, I had three different week-long vacations during which I couldn't do lessons. Even so, when I got back, the tree was still gold. Others have reported similar experiences.

This suggested to me that it is possible to have a durable gold tree without a whole lot of work. That is, it seemed that as few at two general strengthening exercises per day might be enough, if done daily for a long enough time.

Naomi's Italian Trees

My friend Naomi in New Zealand was interested in exploring this, and she agreed to help do a few experiments. She had finished her English-to-Italian tree (aka the "forward tree") in just a few months and wanted to gild it. She had also just completed the Italian-to-English tree (aka the "reverse tree") in a single day and wanted to keep it gold.

The experiment was very simple: On her forward tree, she did two general strengthens per day. On the reverse tree, she did three general strengthens per day. Back when Duolingo allowed you to fail, she would persist until she completed that number, although, as it happens, she rarely failed an exercise.

Here's what happened.

With three general strengthens per day, the reverse tree got worse for about 40 days, leveled off for about a month, and then started improving in an irregular sort of way.

The forward tree decayed steadily, reaching 57 weak skills on day 91. At that point, we changed our strategy.

Starting on day 92, Naomi began doing three skill-specific exercises instead of two or three general ones. She selected the skills to strengthen by picking the weak skills highest in her tree. She applied the same algorithm to both trees.

We only have 13 days of data with the new method, but the results speak for themselves.

This graph shows how many weak skills were left each day after Naomi did her strengthening exercises. This shows that the reverse tree was 100% regilded on day 99 and that it has remained so for six days now. On the present trend, the forward tree will be regilded in two more weeks.

Obviously this strongly suggests doing the per-skill exercises rather than the general ones--just as Duolingo had advised people. In fact, the per-skill exercises appear to be more than three-times as effective at regilding. It also suggests that two exercises per day was not enough.

We adopted one additional rule: substitute general exercises for specific ones if there are no weak skills left, but never do more than two general exercises on the same day. That is, if the tree has any weak skills, then Naomi still does three strengthening exercises--padding them out with general ones as needed, but if the tree was solid gold to begin with, then she only does two generals, not three. The idea is that, like with my French tree, a durable gold tree should eventually need only two per day to maintain it.

Note: Throughout the process, Naomi reported that the algorithm seemed to have a knack for finding exactly the things she was weakest on. She felt the exercise improved her Italian enormously, even if she did spend 91 days making no visible progress on regilding her trees.

Greg's Spanish and Italian Trees

During this time, I let my own Spanish and Italian trees decay. (Both had been gold on day zero of Naomi's experiment.) Over the next month or two I'll try to reproduce the results from Naomi's trees, but I wanted to share one key result that I got on the first day:

For the best learning experience, you should strengthen from bottom-up instead of top-down.

The reason to prefer bottom up is that it drills you in the skills you most-recently learned--the skills you are most likely to need help in. You'll discover that Duolingo has a lot more material for those skills that you never saw when you did them the first time. Most people have a weak grip on the last skills in a tree, so it makes a great deal of sense to prioritize strengthening them first. In contrast, the stuff at the top of the tree is far easier to do, but it's also far less valuable to review.

The exception would be for someone trying to resurrect a long-unused tree or for someone who has become overwhelmed and is considering quitting. Those folks should strengthen from the top down because it's equivalent to starting over, in a way, without losing everything you learned the first time. (In my view, no one should ever delete their Duolingo tree and start over.)

Other Issues

I always advise people to avoid timed practices and not to use the mouse-over hints unless absolutely necessary. I'll explain my reasoning for both suggestions.

Timed Practices

You buy the ability to do timed practices at the lingot store. It's a one-time purchase, but it's still a bad deal. The way it works is that when do a review Duolingo offers you the option to do timed practice instead of the normal kind. In fact, it becomes the default.

In timed practice, you only have a few seconds before the clock runs out and you lose the round. Every correct answer puts more time on the clock, so you need to go like lightening to keep ahead. In theory, this helps you develop the skills to handle conversation in real time.

Many of the people I've talked to who reported doing lots and lots of review lessons with little progress on regilding their trees told me they were doing timed practices. I think this strengthens the tree slowly because time pressure encourages people to skip long sentences. The earlier post from Duolingo said that every word counts, so it would make sense that skipping the long sentences would really hurt you.

Given that Duolingo's new UI is much more forgiving of mistakes, it probably makes more sense to try to get the same effect by simply going through the exercises as fast as you can, accepting the fact that you'll make more errors. As a bonus, when you do make an error, you can stop and study what you did wrong. Anyway, if you want to regild your tree, you should probably stay away from timed practice.

Hints

The other thing that seems to be strongly associated with lack of success is using hints. Using a hint means doing a lesson and mousing over a word to get Duolingo to show you the definition.

Unfortunately Duolingo takes this as a hint that you don't know that word at all, and it makes that word decay faster. Do use the hints if you really don't know the word. (We want to help Duolingo figure out what you really need to study, after all.) But don't use them just because you want to be 100% sure of a word before you press return.

Summary

Plan to do three exercises per day. If you can't invest that much effort, you probably can't do this in a reasonable time. With that, here is the system I recommend for making durable gold trees with Duolingo:

• Always do a skill-specific strengthening exercise if there are any weak skills in your tree at all. Only do a general strengthening exercise if there are no more weak skills to do.
• If there are multiple weak skills to choose from, always pick the one that is furthest down the tree. (That is, prefer skills you learned later over ones you learned earlier.) But, if you are effectively starting over (e.g. after a long absence or because you're overwhelmed) then pick the highest (that is easiest) weak skills first.
• For an incomplete tree, do two strengthening exercises and then do one new exercise every day. If you're not ready for a new exercise, do a third strengthening exercise instead.
• For a complete tree that isn't all gold, do three strengthening exercises every day, using general strengthening exercises if you run out of skill-specific ones.
• For a complete, solid-gold tree, only do two strengthening exercises per day--both of which have to be general ones, of course.

Never do a timed practice. Never use hints.

Finally, take your time. Don't try to regild your tree in a day or two of inhumanly focused effort--followed by a month of neglect. A steady effort over a long period of time is the best way to do this. You'll learn the most that way, and it won't burn you out.

If you follow this plan, assuming that you are doing your best on the exercises, your tree will eventually be "durable gold," meaning it will stay gold with minimal effort on your part, even if you go on vacation for a week or so. How long it will take to get there depends on a lot of things, but a month or two seems typical. (It depends on how well you do the exercises and on how deeply decayed your tree was in the first place.) Have at it, and best of luck!

I would love to hear from anyone who gives this a try. Leave a comment and let me know how it went.