Do dyslexia fonts like OpenDyslexic or Dyslexie work?

No. Controlled studies have tested both against ordinary typefaces and found no improvement in reading speed or accuracy, in children with dyslexia or without. Most children in those studies preferred the ordinary font.

Does wider letter spacing help a child who struggles with reading?

Sometimes, modestly, and not in the way it is usually sold. The most consistent finding is fewer mistakes rather than faster reading, and it helps ordinary readers as much as it helps readers with dyslexia. Widening the gaps between letters without also widening the gaps between words makes reading slower, not faster.

What font should I use instead?

Any clean, plain typeface your child finds comfortable. Nothing in the research points to one winner, so pick the readable, boring option and spend the money elsewhere.

Does Plimmery have a dyslexia font or a dyslexia mode?

No, and that is deliberate. There is a setting that widens letter and line spacing, offered as a comfort option rather than a treatment. Plimmery does not test for dyslexia and gives no result that means anything clinically.

If typography is not the answer, what is?

Teaching. The largest review of the question pooled 66 comparisons from 38 experiments and found a moderate, reliable benefit from systematic phonics, meaning being taught explicitly how letters map to sounds in a sensible order, with a bigger benefit when it starts early.

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Sources checked, one by one

Dyslexia fonts, letter spacing, and what actually helps

If you are about to buy a special typeface for a child who finds reading hard, read this first. It has been tested, more than once, on hundreds of children.

The short version

Typefaces sold as dyslexia aids, OpenDyslexic and Dyslexie chief among them, have been put through controlled studies. Children did not read faster with them. They did not make fewer mistakes. Most of the children tested did not even like them[1][2][3].

Space between the letters is a different question, and a more interesting one. There is something real there. It is smaller than the headlines suggested, it is not specific to dyslexia, and doing it badly makes reading worse.

That distinction is the whole point of this page. One of these is a purchase that changes nothing. The other is a setting you already have, that you can try tonight, for free.

What the font studies found

Three studies, three research groups, three different fonts and languages. Same answer.

OpenDyslexic, against Arial and Times New Roman

Twelve school-age children with a dyslexia diagnosis read letters, real words and made-up words in each font, switching between them. No gain in speed. No gain in accuracy. Not for the group, and not for a single child in it. None of them said they preferred it [1].

Dyslexie, tested twice, on hundreds of children

In the first experiment, 170 children with dyslexia read the same text in Dyslexie and in Arial. Same speed, comparable number of errors, and most of them preferred Arial. A second experiment added 45 children without dyslexia and a third font, and found the same [2].

The letter shapes, pulled apart from the spacing

128 Italian children, half of them with dyslexia, read eight matched texts in which the shape of the letters, the gap between letters and the gap between words were varied separately. The letter shapes did nothing at all [3].

Why the idea sounds so plausible

The pitch behind these fonts starts from something real. Some readers with dyslexia are unusually affected by crowding: a letter is harder to pick out when other letters sit tight against it. Loosen things up, the reasoning goes, and the crowding eases.

The problem is that a specialty font changes two things at once. It redraws the letters, and it sets them further apart. Those are separable, and the Italian study separated them. The spacing is where any effect lives. The shapes carry none of it [3].

A parent who buys the font is paying for the half that does not work.

Spacing: real, smaller than advertised, easy to get wrong

The study that started all of this appeared in 2012 [4]. Italian and French children with dyslexia read text set with extra-large gaps between the letters, and their reading improved on the spot, with no training of any kind. The authors put it down to crowding. It was a striking result and it travelled fast.

What came afterwards is the part the marketing leaves out. A Dutch team ran it again while holding the length of the sentences constant, which the original had not done [5]. They found something narrower. Children made fewer mistakes with wider spacing, but read no faster. Children without dyslexia benefited just as much, so this is a legibility effect rather than a dyslexia treatment. And it only showed up when whole sentences were on screen, not when words came one at a time.

The Italian study went further still and found no general speed advantage from wider spacing in either group. It also found a cost: when the letters were spread out without spreading the words out to match, reading got slower [3]. That makes sense once you picture it. A word stops looking like a word when the gaps inside it are as wide as the gaps around it.

So where does that leave spacing?

It can reduce mistakes. That much has held up.
It probably will not make anyone read faster.
It helps readers in general, not readers with dyslexia specifically.
Widen the word gaps along with the letter gaps, or you will make things worse.
It is a comfort adjustment. It is not treatment, and no reputable study calls it that.

What does move the needle

Typography is a comfort question. Teaching is the answer to the real one. The largest review of that question pooled 66 comparisons from 38 experiments and put the overall benefit of systematic phonics, meaning being taught explicitly how letters stand for sounds in a deliberate order, at an effect size of 0.41 [6].

Effect size is just researchers' shorthand for how big a difference something made. 0.41 is solid and unspectacular: the kind of gain you see across a whole class over a year, not the kind that transforms one child in a fortnight. The same review found the benefit larger when the teaching starts early, 0.55, than when it starts later, 0.27. If you are choosing where to put your energy, that is where the evidence points.

What we do about it

Plimmery does not ship a specialty dyslexia typeface, because the evidence does not support one.
There is a setting in the parent view that widens letter and line spacing. It is there as a comfort option. It is not offered as treatment, and the studies above are the reason it adjusts spacing rather than swapping the font.
Plimmery does not test for dyslexia and gives no result that means anything clinically. If you are worried about how your child is going, the honest place to start is a conversation with their teacher.
An app supplements teaching. It does not replace a teacher and it does not replace you. We put the numbers behind that in what an app is actually worth.

Questions parents ask

Do dyslexia fonts like OpenDyslexic or Dyslexie work?: No. Controlled studies have tested both against ordinary typefaces and found no improvement in reading speed or accuracy, in children with dyslexia or without. Most children in those studies preferred the ordinary font.[1][2][3]
Does wider letter spacing help a child who struggles with reading?: Sometimes, modestly, and not in the way it is usually sold. The most consistent finding is fewer mistakes rather than faster reading, and it helps ordinary readers as much as it helps readers with dyslexia. Widening the gaps between letters without also widening the gaps between words makes reading slower, not faster.[3][5]
What font should I use instead?: Any clean, plain typeface your child finds comfortable. Nothing in the research points to one winner, so pick the readable, boring option and spend the money elsewhere.
Does Plimmery have a dyslexia font or a dyslexia mode?: No, and that is deliberate. There is a setting that widens letter and line spacing, offered as a comfort option rather than a treatment. Plimmery does not test for dyslexia and gives no result that means anything clinically.
If typography is not the answer, what is?: Teaching. The largest review of the question pooled 66 comparisons from 38 experiments and found a moderate, reliable benefit from systematic phonics, meaning being taught explicitly how letters map to sounds in a sensible order, with a bigger benefit when it starts early.[6]

References

Every source below was opened and read before it was cited. Where a figure was not visible in the source we could reach, we left it off the page rather than repeat it secondhand.

[1] Wery, J. J., and Diliberto, J. A. (2017). The effect of a specialized dyslexia font, OpenDyslexic, on reading rate and accuracy. Annals of Dyslexia, 67(2), 114 to 127.
doi.org/10.1007/s11881-016-0127-1
What we confirmed: Abstract and participant details read in full. Single-subject alternating-treatment design, 12 school-age students with dyslexia (grades 3 to 6), OpenDyslexic against Arial and Times New Roman across letter naming, word reading and nonsense-word reading. No improvement in rate or accuracy for the group or for any individual, and no participant reported preferring the font.
[2] Kuster, S. M., van Weerdenburg, M., Gompel, M., and Bosman, A. M. T. (2018). Dyslexie font does not benefit reading in children with or without dyslexia. Annals of Dyslexia, 68(1), 25 to 42.
doi.org/10.1007/s11881-017-0154-6
What we confirmed: Abstract and both experiment summaries read in full. Experiment 1: 170 children with dyslexia read equally fast in Dyslexie and Arial with a comparable error count. Experiment 2: 102 children with dyslexia and 45 without, three fonts, same result. Font preference was unrelated to reading performance.
[3] Galliussi, J., Perondi, L., Chia, G., Gerbino, W., and Bernardis, P. (2020). Inter-letter spacing, inter-word spacing, and font with dyslexia-friendly features: testing text readability in people with and without dyslexia. Annals of Dyslexia, 70(1), 141 to 152.
doi.org/10.1007/s11881-020-00194-x
What we confirmed: Author manuscript read in full, including the discussion. Two groups of 64 Italian children, with and without dyslexia, read 8 matched texts. The letterform produced no effect. No general reading-speed advantage from increased spacing in either group, and reading speed was impaired when inter-letter spacing rose without a matching rise in inter-word spacing.
[4] Zorzi, M., Barbiero, C., Facoetti, A., Lonciari, I., Carrozzi, M., Montico, M., Bravar, L., George, F., Pech-Georgel, C., and Ziegler, J. C. (2012). Extra-large letter spacing improves reading in dyslexia. Proceedings of the National Academy of Sciences, 109(28), 11455 to 11459.
doi.org/10.1073/pnas.1205566109
What we confirmed: Abstract read in full. Reports that a simple manipulation of letter spacing substantially improved text reading on the fly, with no training, in a large unselected sample of Italian and French children with dyslexia, attributed to crowding. Participant counts and the size of the gain were not visible in the sources we could open, so no figures from this study are quoted on this page.
[5] Hakvoort, B., van den Boer, M., Leenaars, T., Bos, P., and Tijms, J. (2017). Improvements in reading accuracy as a result of increased interletter spacing are not specific to children with dyslexia. Journal of Experimental Child Psychology, 164, 101 to 116.
doi.org/10.1016/j.jecp.2017.07.010
What we confirmed: Abstract read in full from the author manuscript. Experiment 1: 30 children with dyslexia and 30 controls, mean age 9 years 11 months. Experiment 2: an unselected sample of 189 readers, mean age 9 years 3 months. Increased letter spacing produced fewer errors and no change in reading rate, affected both groups in similar ways, and only appeared when complete sentences were shown rather than one word at a time.
[6] Ehri, L. C., Nunes, S. R., Stahl, S. A., and Willows, D. M. (2001). Systematic phonics instruction helps students learn to read: evidence from the National Reading Panel's meta-analysis. Review of Educational Research, 71(3), 393 to 447.
doi.org/10.3102/00346543071003393
What we confirmed: Abstract read in full. 66 treatment-control comparisons from 38 experiments. Overall effect of systematic phonics on reading d = 0.41; d = 0.55 when instruction began early and d = 0.27 when it began after first grade.

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