How to study from lecture slides (and why rereading them isn't enough)

If you want to study from lecture slides, reading them from start to finish won't do it. A slide deck isn't a textbook: it's the script your professor used to talk for two hours, and half of what mattered was in what they said, not in what they wrote. That's why you get to the last slide and feel like nothing stuck.

The good news is that it's fixable, and the fix isn't more hours in front of the screen. It's changing what you do with each slide: rebuild what's missing, explain it in your own words, and force yourself to recall it without looking.

Here's the method I use as a final-year computer engineering student, after years of preparing for almost every exam from decks of more than a hundred slides.

Why rereading slides doesn't work

A slide is designed to support someone who is talking. It has a title, three or four short lines, maybe a chart. In the lecture that's enough, because the professor connects the ideas, gives the example and explains why it matters. When you open it alone a week later, what you have are the keywords of an explanation that's gone.

Reading it like that has two problems:

• It gives you a false sense that you know it. Recognizing a line ("oh right, we covered this") is not the same as being able to explain it. Recognition is easy and misleading; the exam asks for the other thing.
• Nothing forces you to think. One slide after another, eyes skimming, is the fastest way to reach slide forty without remembering slide twenty.

Step 1: skim the whole deck before you study it

Before going into detail, flip through the whole thing in ten minutes. Not to learn it, but to see the map: how many topics there are, where each one starts, which slides are just titles or examples and which carry the heavy content.

Write down the three or four big blocks on a sheet of paper. Now it isn't "eighty slides" anymore, it's four topics of twenty, and each one fits in a single study session.

Step 2: rebuild what the professor said

This is the step almost nobody does, and the one that changes the result the most. For every slide with content, ask yourself: if this is all they wrote, what did they explain out loud?

Some clues to rebuild it:

• Single words are concepts that need a definition. If the slide just says "latency", the lecture explained what it is and why it matters. Write that down.
• Arrows and diagrams are relationships. An arrow from A to B is a "because", a "so" or a "turns into". Say which one.
• Examples can be invented. If there isn't one, come up with your own. If you can't think of any, you don't understand it yet.

For whatever you can't rebuild, use your lecture notes, the course textbook or a classmate. What matters is that every slide ends up with its full explanation, not three words.

Step 3: explain it out loud, in your own words

Cover the slide, or only glance at it, and explain it as if you were telling a friend who skipped that lecture. Out loud, not in your head: in your head everything seems clear; out loud the gaps show up right away.

If you get stuck, don't push through. Go back to the slide, understand the missing piece and explain it again. This back and forth feels slow at first, but it's exactly the work that saves you on exam day.

A trick that works: explain each slide by answering three questions. What is it, why does it matter, and how does it connect to the previous one. If you can answer all three, that slide is done.

Step 4: quiz yourself without looking

When you finish a block, close the deck and try to recall what you saw. Write down everything you remember about the topic, or ask yourself the kind of questions your professor might put on the exam and answer them without peeking.

This is called active recall, and it's one of the best-supported findings in the research on how we learn: the effort of pulling something out of memory is what makes it stick. Rereading, on the other hand, feels productive and leaves very little behind.

Then compare with the slides. Whatever you forgot or got wrong is exactly what you need to study again, and now you know precisely what it is, instead of rereading everything.

Step 5: come back a few days later

What you studied today will be blurry in a week. That's not a you problem, it's how memory works. The fix is to quiz yourself on the same topic the next day, three days later and a week later, with less effort each time.

You don't need to study everything again. Just repeat step 4: ten minutes of recalling without looking and checking what you missed. Do it this way and the night before the exam becomes review instead of learning from scratch.

Tools that help (and when to use them)

The method works with a pen and paper. But some steps can go faster:

• To rebuild what's missing (step 2), anything that explains the slide works: your notes, a video on the topic, a classmate or an AI. If you use a chatbot like ChatGPT, ask it to explain the slide rather than summarize it, and check what it says against your material, because it sometimes fills gaps with things that weren't there. I go into more detail in the ChatGPT vs Filmina comparison.
• For long decks you can't bring yourself to start, I built Filmina: a Mac app that explains every slide out loud, pointing at the part it's talking about, as if you had the lecture again. Everything runs on your Mac and the PDF is never uploaded. You still have to do steps 3 to 5 afterwards: nobody learns just by listening.
• For step 5, any spaced repetition system works, from paper cards to flashcard apps. What matters is that it makes you recall before you see the answer.

A plan for an 80-slide deck

To make it concrete, here's how I'd split a big deck across a week before a midterm:

That's less time than you'd lose rereading the deck three times, and you walk in knowing what you know and what you don't.

Frequently asked questions

Is it better to study from slides or from the textbook?

It depends on the course, but the slides tell you what your professor thought was important, which is usually what gets tested. The best approach is to use the deck as your guide and the textbook to fill in what the slides don't explain.

Should I print my lecture slides to study?

Printing helps if you're going to write on them, adding what the professor said on each one. If you're only going to read them, paper or screen makes little difference: what matters is explaining them and quizzing yourself without looking.

How long does it take to study a 100-slide lecture?

With the method in this post, somewhere between six and ten hours spread over several days, depending on how dense it is. Cramming it into one night takes almost as long and fades much faster.

How do I study slides that have almost no text?

Those are the ones that need step 2 the most. Use your notes, the textbook or an outside explanation to rebuild what was said in the lecture, and don't consider them studied until you can explain them without looking.