# When should I scrap my projector for a blackboard?

These days, we've got all this fancy, new-fangled technology. We've got live coding, we've got presentations, we've got remote desktop adapted for classroom use. There seems to be a tool for every teaching problem. But when should we ignore the KnowledgeInjector2000TM and instead use the good old blackboard?

More specifically, which concepts are easier to explain with a blackboard and how would you use a blackboard to explain them?

• Does it have to be black board, or would you like other unplugged ideas? Jun 16 '17 at 15:57
• @richard Based on the context of this question (and the presence of other unplugged discussions), I think this question specifically focuses on projector v. board. Jun 16 '17 at 16:51
• Alternatives I've seen are using a tablet pen to write/draw on-screen, and a desk-mounted camera to project writing from a sheet of paper. Both were far more readable than a blackboard in a large lecture theatre where many students can be sitting far back.
– Bob
Jun 16 '17 at 17:02
• I used to like TurboSee, but it is passe these days. I loved Indoctrinator++. Not so sure about Lava (its a wash). Now I use Look#, it improves my image.
– user737
Jun 16 '17 at 17:15
• Just leaving these links here; anyone feel free to turn them into an answer if appropriate: Psychophysiology of blackboard teaching by Borovik, Still Like That Old-Time Blackboard Talk by Zeilberger. Jun 17 '17 at 23:22

Shifting to the blackboard/whiteboard from the projector serves two main purposes:

• Slows down the pace of instruction. I can type much faster than I can write on the whiteboard. However, this is not always a good thing. When I'm discussing something complex or want to ensure my instruction does not move too quickly, I shift to writing things out. This forces me to be more thoughtful with timing and often times has prevented me from giving students more information than was necessary for a particular lesson.

• Shifts focus from code to concept. As I say in a lot of my answers, differentiation is key. Staring at code to understand a concept is not always going to make it sink in. By writing on the board, I often times can draw close attention to a concept (i.e. recursion or variables) outside of its context within a program. When introducing something new and/or something complex, this helps me ensure that students understand the thing before they code that thing. For example, with recursion, I draw out stack frames, naming each one with its function name and arguments and drawing arrows with values passed in and values returned. The magic of a few lines of code that calculates a factorial becomes a little less opaque when there's a visual abstraction to which students can connect the code. Additionally, introducing variable assignment to beginners, especially something like x = x + 1;, works well on the whiteboard where I can number the steps, translate it into "English" underneath, use different colors, etc.

Bonus: It's not always a game of either/or. Projecting code onto a whiteboard mixes the modalities: students can see "real code," but that same code can then be analyzed and annotated by hand.

For my own unique context in a classroom with whiteboard-top desks, I can have students write down what I write down when I use the whiteboard. It becomes a shared task since we are all doing the same thing and forces me outside of the "sage on the stage" paradigm for a minute. Instead of lecture and fast-typing, I can participate along with them in writing on a whiteboard. This has as much to do with engagement and classroom environment as it does with pedagogy.

• The whiteboard-top desk is an interesting idea. What is next, the screen-desks from Ender's Game? (I wrote a program a long time ago to march letters around the edge of my screen...)
– user737
Jun 16 '17 at 17:11
• Whiteboard desks are awesome. Mine aren't specifically whiteboard painted but they work with dry erase markers. I have an Expo marker on me all the time and can write on the desk to help. Jun 17 '17 at 21:01

I'm working in TCS, so my lectures are relatively mathematical. For me, it's a rather clear split:

• Definitions, Inference Systems, etc.: Projector (+ lecture notes)
• Lemmas, Theorems: Projector (+ lecture notes)
• Proofs: Blackboard (+ lecture notes)
• Examples: Blackboard

• I save some time compared to a blackboard-only lecture.
• I can refer to definitions and lemmas on the projector while presenting proofs or examples on the blackboard (while proving Thm. 3.7: "... and now we can use Lemma 3.4 [shows Lemma 3.4 on the projector] and we get a contradiction ...")
• I have the necessary amount of space for proofs (much more than using a projector).
• I present proofs and examples at a reasonable speed.
• I can point to the blackboard with my hands, which is much more effective than using a laser pointer ("... and now we compare this subterm [marks some text with the left hand] and that subterm [marks some text with the right hand] ...").
• I can improvise examples whenever necessary.
• Definitely, the ability to point, etc is a huge advantage. Getting a bunch of light projected on oneself is not.
– user737
Jun 16 '17 at 17:06
• @nocomprende Fortunately, my projector and my blackboard don't overlap too much. (If you can't use them in parallel it sucks.)
– Uwe
Jun 16 '17 at 17:11

My poor blackboard1 only gets light use nowadays, I'm afraid. Coding examples are usually too large to put up there, all of my intricate diagrams are clarified with (judicious!) animations in PowerPoint, and my debugging gets demonstrated live on the projector screen. The humble blackboard has seen its role reduced in CS classrooms as the years have gone by.

It still has its place, though! Improvised diagrams go up there, such as when a student asks an unexpected question about a linked list. And pulling a struggling kid up to the board (during individual work time, not as some form of humiliation) can give us space, both mental and physical, to work through a conceptual problem together.

Of course, in more advanced CS coursework, we start veering back towards the mathematical, where the blackboard is still king. Well, maybe not the king anymore, but at least a Marquess or an Earl. Working through problems and proofs at the blackboard keeps the pace slower than a PowerPoint and gives the students that much more time to absorb the material, and asking students to write up the answers to in-class questions allows us to have class discussions around the results.

And there's one more place where the board comes in handy: harder labs, especially the kind that kids have a hand in designing themselves. I've found that my students naturally gravitate to the board when they need to brainstorm or work through a particularly tricky problem. Something about having all that space to think and try frees the mind. Paper just doesn't seem to do this same trick.

The blackboard may be dying, but it ain't dead yet.

1 Okay, technically I use a whiteboard in my classroom. I'd prefer a blackboard, but I don't get that choice in real life. But I get my choice here and now, in this very answer, and blackboard, I choose you.

• +1 Improvising is something I often find easier with a blackboard than with computer tools (for example, modifying a presentation). Jun 16 '17 at 14:27
• I liked the reference at the last sentence in the footnote ;) Jun 16 '17 at 14:27
• Greenboards and brownboards are nice, too. We also have SmartBoards and someone here experimented with a "SmoothBoard" (touch-sensitive board on any wall).
– user737
Jun 16 '17 at 15:26

One example is the front end web development concept of the box model. For those who do not know what the box model is, here is a graphic:

I find that there is no real way to explain it without drawing it out. Usually, when I teach this, I've already covered basic HTML and CSS syntax, including a few properties (e.g. background). I like to give the example of creating a span with some text inside, so I draw on the board:

Hello Class!


I'll then explain that the browser sees that as the "content" of the element, and draws a box around it, so I draw a box around it:

|---------|
| Content |
|---------|


I'll also point out that the browser draws a box around the entire element:

|-----------------|
|                 |
|   |---------|   |
|   | Content |   |
|   |---------|   |
|     Element     |
|-----------------|


Then I'll explain that the browser need to how much space to give the element on the outside and how much space it needs to give the content, which introduces padding and margin, and finally I'll add a border, finishing my explanation.

• I find this is a good usage of a blackboard, but I think (I'm not at all sure of this) that chrome can show this for a website when you press F-12... Jun 16 '17 at 14:21
• @ItamarGreen Yeah, most dev tools in your browser will show it, but a) it's small and b) I don't want to just show the picture, the blackboard helps me explain it. Jun 16 '17 at 14:22
• Which is why this is a good answer ;) Jun 16 '17 at 14:23

The last time I used a whiteboard as a whiteboard was to describe a maze building algorithm. It was a small-ish board that I put on the ground and drew a grid. I then stepped in a square and we walked (literally and algorithmically) through the algorithm where I built the maze.

The whiteboard on the front of my room gets used sometimes when I want to write over examples. I'll project and then annotate what's there. But that's rare, and it's usually covered up with a large projector screen.

Of course, my handwriting is terrible and my classroom is large enough that it's tough to see anything I write from the back. So that's probably part of the reason.

Somewhat related story here...

When I interviewed, before I saw the classroom, the AP that was interviewing me was very apologetic that there wasn't a Smartboard in the classroom. They had just gone through a rebuild and reconfigured most of the classrooms, and most had a Smartboard. Mine had "just a normal screen." When I walked in I was good with the screen. It's almost floor to ceiling and covers probably 80% of the width of my room. Much better than a little Smartboard.

• Yes! Project ON the whiteboard, and write on it. This is my main mode of lecturing. I have a page scan thing that I can project the textbook or other printed material, and I can connect to the computer to project that, and switch back and forth. The whiteboard is always there, so I can even leave notes up when I am not lecturing (projector is off). Why anyone would do anything different is beyond me.
– user737
Jun 16 '17 at 17:09

You can use a blackboard with a fun on board example:

A good way to explain what the computer does while executing a recursive method, is to debug a (simple) recursive method. This is done by hand (on the blackboard) by going through the method line by line, and with every recursive call, going down 1 line (on the board) and indenting. Then going through the method line by line, with the parameters passed from the recursive call.

This is done recursively, and when a return statement is met, you go down 1 line (again, on the board) and "unindent".

This is great way to explain recursion. The students see on the board the process done by the computer. While drawing it on a computer and projecting it does show the final result, the process itself might be lost on the students.

There is also some value to seeing how the call stack works, but that's a side bonus.

Another nice bonus to this is a situation where one runs out of space while going down lines on the board. That's when the instructor should turn dramatically towards the students and say "And that, is what stack overflow means."

• If the end of the board is reached while indenting, you could even explain a stack overflow with this. Jun 16 '17 at 14:23
• @TuringTux good point. Thanks (I'll add it to the answer. Do you want me to give you credit for that?) Jun 16 '17 at 14:23
• No, you don't need to :) Nice to see I could bring in something valuable. Jun 16 '17 at 14:25

There may be a psychological-physiological learning advantage to having students see solutions or code presented at nearly the same rate as the student would write or type in the code themselves.

Having N steps appear (especially if it exceeds 7+-2 cognitive units), all at once, might overload a student's short term memory, and thus can result in some of the information being nearly invisible, and thus harder to learn from that projection.

An alternative would be to use presentation software to animate the projection so that the code (or algorithms, etc.) appears sequentially in time at a slow enough rate to talk through each step or component.