Back to the on-screen lesson ·
Why the strategies that work feel worse, how to tell a desirable difficulty from one that is only in the way, and how to tune a session.
Paper packet. Every task here also exists on screen, where it is checked automatically; answers written on paper are not assessed by Nydus. When you are back at a device, enter your answers there.
You will read a mismatch between how a session felt and what a later check showed, sort difficulties into desirable and not, and adjust a plan toward effortful success.
Every strategy so far has a catch: it feels worse. A blank page shows you what you do not know; a gap means some of it has slipped; a mixed set is slow and full of wrong turns. This lesson explains why that is the point, how to tell a useful difficulty from a useless one, and how to adjust a plan that has become too hard or too easy.
| Term | What it means |
|---|---|
| Performance | How well you do during or just after a session, with the material fresh. |
| Learning | What lasts: what you can still do days or weeks later. |
| Desirable difficulty | A difficulty built into how you practice that you can meet with effort, such as retrieval, spacing or mixing. |
| Undesirable difficulty | A difficulty that makes studying harder and practices nothing: noise, exhaustion, illness, material far beyond you. |
| Effortful success | Getting most answers with real effort — the zone a session aims for. |
Bjork and Bjork (2011) separate two things a study session can show. Performance is how well you do right now. Learning is what is still there next week. They often move in opposite directions. Rereading and blocked practice make performance high and the session smooth; retrieval, spacing and mixing make performance lower and the session effortful, and they are the ones that hold up later.
They call the second kind desirable difficulties: retrieving instead of rereading, spacing instead of massing, interleaving instead of blocking, and varying the conditions of practice. The word desirable carries a condition. A difficulty is desirable only if you can meet it — with effort, most of the time. A blank page that produces nothing, after a gap so long that everything has gone, is not desirable; it is just hard.
So aim for effortful success. If almost nothing comes back, make it easier: restudy, shorten the gap, add a cue. If everything comes back instantly, make it harder: lengthen the gap, mix more. And some difficulties are never desirable at all.
Another way: picture
Think of weight training. A weight you lift easily builds nothing, and one you cannot lift at all builds nothing either. The useful weight is the one you can lift with effort.
Another way: steps
In study after study, people judge the less effective strategy the better one. Roediger and Karpicke (2006) found students who reread more confident than students who practiced recalling, though the recallers remembered more a week later. Kornell and Bjork (2008) showed people paintings by different artists, either grouped by artist or mixed; mixing helped them name the artist of new paintings, yet most participants rated grouping as equally or more effective. Kornell (2009) found spacing beat cramming for about 90 percent of the participants in a flashcard study, while about 72 percent believed cramming had worked better.
The feeling of ease is real. It is a report on how smoothly the material is going right now, with it in front of you. It is a poor guide to next week, and it is the only signal most people check. A later check, after a gap, is the better one.
Some difficulties make studying harder and practice nothing. Noise, a phone buzzing, a room that is too hot. Exhaustion, illness, pain, grief. Material that needs background you do not have yet, so no amount of effort gets you anywhere. None of these is a sign that the session is working, and none should be pushed through. If you are ill or worn out, stop: the schedule's missed-session rule from lesson 4 is there for exactly this, and the session moves to the next free day.
Here is a rough rule for the retrieval sessions in this course — a rule of thumb, not a research finding. Count the percent of questions you got right before looking. Under about half: the gap was too long or the first study too thin, so restudy and halve the next gap. Between about half and nine in ten: effortful success, keep the plan. Over nine in ten, with every answer instant: double the next gap or mix in more kinds.
Bjork and Bjork (2011) describe a classic study by Kerr and Booth (1978). Children practiced tossing beanbags at a target on the floor. One group always threw from the distance they would be tested at, 3 feet. Another group never threw from 3 feet: they practiced from 2 feet and 4 feet, mixed. On the final test at 3 feet, the mixed group was more accurate — although they had never practiced from that distance.
A fictional high-school basketball player, Jaylen, uses the same idea. Instead of 50 free throws from the line, he shoots from the line, one step in and one step back, in a mixed order. His percentage during practice drops, and it feels worse. He logs his game free throws each week instead of his practice percentage, because the games are the later check.
"If it feels hard, it is working." Only if the difficulty comes from how you practice and you can meet it. Studying while exhausted is hard and does nothing useful.
"A smooth session means I learned it." A smooth session measures performance with the material in front of you.
"Getting things wrong in practice is bad." Errors during retrieval and mixed practice are expected, and each one is corrected by the check.
"Harder is always better." If almost nothing comes back, the session is too hard to learn from. Make it easier until effort is rewarded.
Write down how each session felt.
Blocked algebra: easy, 18/20. Mixed algebra: slow, 12/20.
The feeling and the session score are performance.
Write down the later check.
One week later, mixed check: blocked topics 8/20, mixed topics 14/20
The later check, after a gap, is closer to learning.
Compare the change for each.
Blocked: 18 → 8, down 10. Mixed: 12 → 14, up 2.
The easy session lost the most; the hard one held.
Name the difficulty and keep it.
Interleaving: desirable. Next week: mixed sets again.
The log, not the feeling, decides the plan.
Record the result.
Spanish list after a 10-day gap: 3 of 20 → 15 percent
Almost nothing came back, so the difficulty was not one she could meet.
Make it easier this time.
Restudy the list; answer again with first letters as cues
A cue brings the answers into reach, so the effort is rewarded.
Shorten the next gap.
Next session: in 5 days, not 10
Half the gap, by the working rule.
Plan to take the support away.
In 5 days: no cues; if above half right, gaps grow again
The aim is effortful success, then more difficulty as it holds.
Record the result.
Biology terms after a 2-day gap: 20 of 20, all instant
Nothing had slipped, so the session asked very little.
Name what to change.
Lengthen the gap, and mix in terms from the last unit
Spacing and mixing both add a difficulty she can meet.
Set the next session.
A fictional student practices chemistry problems two ways. Blocked: 18 of 20 right during the session, and it felt easy. Mixed: 12 of 20 right, and it felt slow. A week later, on a mixed check, she gets 7 of 20 on the blocked topics and 14 of 20 on the mixed ones. What does the mismatch tell her?
In Kornell's 2009 flashcard study, spacing beat cramming for about 90 percent of the participants, yet about 72 percent believed cramming had worked better. Suppose a fictional class of 150 students matched those percentages. Complete the worked count.
Find how many did better with spacing.
90% of 150 = a students
This is what the later test showed.
Find how many believed cramming worked better.
72% of 150 = b students
This is what the students felt after studying.
Compare the two counts.
Most did better with spacing; most believed the opposite.
Judging by feel would have led most of the class to the weaker strategy.
Five difficulties from a fictional student's week. Mark each **desirable** or **not desirable**.
| Verdict | |
|---|---|
| Writing answers from memory | |
| A leaf blower outside all session | |
| Coming back after four days | |
| Studying at 1 a.m. after a double shift | |
| Two months away, none of it comes back |
A fictional student uses this lesson's working rule: under 50 percent right, halve the next gap; 50 to 90 percent, keep it; over 90 percent, double it. After a 10-day gap, she gets 10 of 25 questions right. What percent is that, and what is her next gap in days?
Percent right: a
Next gap: b days
Four study moves from Bjork and Bjork's list of desirable difficulties. Name the kind of difficulty each one adds.
| Kind of difficulty | |
|---|---|
| Question list before opening the notes | |
| Reviews on day 3 and day 8 | |
| Shuffled cone, cylinder and prism problems | |
| Free throws from three different spots |
A fictional nursing student's log from four study sessions on drug classes. For each, choose what to do next.
| Next step | |
|---|---|
| 2 of 20 after a 12-day gap | |
| 20 of 20, all instant | |
| Exhausted after a night shift | |
| 13 of 20 with real effort |
Lesson test: one question per skill, one attempt each, no hints. Your answers are checked when you submit.
A fictional student's log. Spanish vocabulary studied by rereading: 90 percent right at the end of the session, 40 percent a week later. Studied with the list covered and answered from memory: 70 percent at the end of the session, 60 percent a week later. Fill in the points lost for each, and whether it held up better.
| Points lost | Held up better? | |
|---|---|---|
| Rereading | ||
| Answering from memory |
You can tell a difficulty worth keeping from one to remove. Look at your last study session: write how it felt, then plan a check after a gap to see what held. Next: asking why, and answering it. You can stop in the middle of any of this. Closing the page is the whole of stopping — your place and anything you had typed are already saved, and the lesson opens again where you left it.
12. Your turn: a session that was too easy, step 3
Next: in 4 days, mixed with unit 2
Doubling the gap follows the working rule for over nine in ten.