7 Common Mistakes When Creating Educational Slide Decks

Two slides into a lecture, half the room is looking at phones. It is tempting to blame the audience, the hour, or the topic. More often the deck itself is doing three jobs at once — notes, handout, script — and none of them well. Weak educational slides rarely come from a lack of design talent. They come from a handful of small decisions made early, before anyone opens a template.

Here are the seven mistakes I see most often in teaching decks, and the fix for each. None of them require new software or a free weekend.

Mistake 1: Building a document instead of a deck

A teaching slide often starts life as a paragraph from a lecture note. Someone pastes it in, shrinks the font, and calls it done. The result is a document projected on a wall: technically readable, practically useless at a distance.

Slides should carry the claim; you carry the explanation. If a slide reads "The Treaty of Versailles imposed reparations that crippled the German economy and fuelled political resentment for a generation," you have written your sentence on the wall and now have nothing left to say. Put "Versailles: punishment or peace?" on the slide and keep the sentence for your voice. Students look up, hear the reasoning, and connect the two.

The read-it-back test

If a student could skip the lecture and get the whole lesson by reading the slides, the deck has replaced you instead of supporting you. Move the detail into a handout or a shared document, and keep the deck for what genuinely needs to be said out loud.

Mistake 2: Leaving every idea on the same slide

Clutter is rarely one bad choice. It accumulates: a logo, a date, a decorative border, four bullets that grew sub-points, a screenshot with a caption. By the fifth element, the audience is reading instead of listening.

Give each slide one job. If you cannot summarise it in a short sentence, it is probably two slides. Cut whatever would not change what you say if it disappeared — then look at the cut version before adding anything back.

These are the usual offenders:

• Full-sentence bullets that you then read aloud
• Two diagrams on one slide "so students can compare" — comparison works better as two slides with a question in between
• Long quotations in small type. Show four words, say the rest.
• Repeated headers, dates and course codes on every slide
• Background images sitting behind body text

Whitespace is not wasted space. It is what tells the eye where to start.

Mistake 3: Design choices that quietly shut people out

Readability in a lecture hall is not the same as readability on your laptop at arm's length. Body text below roughly 24 point fails for anyone in the back five rows, and for anyone with low vision sitting anywhere. Set a floor and hold it, and accept the fewer words per line that follow.

Contrast matters just as much. Light grey text on white looks refined on a monitor and vanishes under a washed-out projector lamp. Colour also carries meaning on charts, and roughly one in twelve men has some form of colour vision deficiency. Pair colour with shape, labels or line style, so a red line and a green line are also a solid line and a dashed one. Add short alternative text to any image that carries information, so the deck still works when it is shared, printed or read by a screen reader.

Mistake 4: Pacing that flatlines

A deck where every slide has the same density, the same layout and the same tempo leaves no room for emphasis. Fifty minutes of identical slides is exhausting, even when each one is well made.

Budget by weight, not by count. A slide introducing a hard concept may deserve four minutes of talk; a single striking image may deserve ten seconds and a pause. If you have 25 slides for a 50-minute class, that averages two minutes each — but the average misleads you. Decide which slides are anchors and which are breathers.

Then build in deliberate changes of rhythm: a slide containing nothing but a question, a short pause after a difficult proof, a quick show of hands. Leave time at the end, too. A deck that runs to the final second has no room for the summary students actually remember.

Mistake 5: Letting decoration compete with the content

Animation is useful when it reveals sequence: the steps of an equation, the stages of a process, the parts of a diagram appearing as you describe them. It is a distraction when text spins in from the left because the effect happened to be in the menu.

Use one accent colour, two typefaces at most, and a single layout family. Drop clip art that adds nothing, shadows that reduce legibility, and transitions that make the audience wait. A simple test: if removing an element makes the slide clearer, remove it.

Mistakes 6 and 7: Skipping the rehearsal, and never revising

Slides that look fine on a laptop can fail in the room. A missing font, a video that will not play, a cable that does not fit, a projector that crops the bottom ten percent of every slide. Walk through the deck once in the actual room, on the actual equipment, with the actual clicker. Open the first slide and the last slide before students arrive, and keep a backup copy as a PDF.

The last mistake is the quiet one: never revising. After class, spend three minutes with the deck open. Which slide did you skip? Where did people squint, lean forward or stop writing? Which slide did you talk over for far longer than planned? Note it in the speaker notes and fix it before the next run. A deck taught four times is usually twice as good as the one built in a single afternoon — but only if the revisions actually happen.

A five-minute pre-flight check

Before you present, run through this list. It catches most of the problems above without any redesign work.

1. Read each slide's headline aloud. Does it state a claim, or just a topic?
2. Find the smallest text in the deck. Is it at least 24 point?
3. Look at the densest slide. Can you split it in two?
4. Squint at the screen from the back of the room. Is anything invisible?
5. Confirm that each animation earns its place.
6. Time the deck out loud, including the pauses you plan to take.
7. Open the file on the presentation machine, not only your own.

Good teaching slides are unremarkable in the best sense: nobody notices them, because the attention stays on the idea and the person explaining it. Fix these seven habits and the deck stops competing with your teaching and starts carrying it.

Photo: RonaldCandonga / Pixabay