A lecturer who is speaking and writing on a chalkboard (or equivalent) usually knows the lecture well and is writing to emphasize and explain key points.
A lecturer who is using PowerPoint often does not know the lecture well, and is trying to hide behind the slides or use them as notes to remember what to say.
Both may be experts about the domain they are discussing, but much more often the chalkboard presenter knows the lecture being given.
1. For displaying text, graphics, animations, etc a powerpoint presentation is great.
2. The chalk board is great for pulling out important equations that will be used throughout the lecture (not lost on slide changes) and to interactively work through a problem. You can draw something out and then ask students what to do next and then execute.
3. Overhead slides are great to manipulations on complex forms. For instance showing how a parser works on a piece of text you can use a pen to mark up the text. Or to show how different actions can effect a system. For instance if we increase the interest rate, the line moves like this etc. This allows you to answer questions in real-time in a visual way.
My favorite video lectures are Gilbert Strang teaching Linear Algebra with nothing but a piece of chalk and a whole lot of chalkboards (the kind that slide up and down, revealing other chalkboards underneath). I can't think of any way those lectures could be improved by any sort of technology.
If a professor understands this, they can use it effectively as a skeleton of a lecture which persists aiding students' intuition of the hierarchy of the material. If a professor, who may well understand the material, doesn't catch the information dearth of PP, they often only end up presenting a small part of the material.
When you have subjects like mathematics and physics purely chalkboard whiteboard lectures is the only thing that works, even classes that are based heavily on either really need a chalkboard.
A mix can work well when the lecturer needs to represent a large amount of diagrams and concepts but still needs to explain how to work out complicated concepts, like example problems. (This is usually where the lecturer really knows a subject.)
For what it's worth, I have a degree in Maths, a PhD in Physics and I am develop software for research purposes, when I don't teach - so I have some experience.
The best way for a student to learn these hard technical subjects is for them to sit with their colleagues and go through group exercises, alongside a lot of hard individual work. The teacher's job is merely to help them over the hurdles they have difficulty with, and to show them the things that are truly worth learning. Although I never went through it myself, I suspect that the Oxbridge system of having indiviual tutoring sessions in small groups as the basis of the teaching is probably perfect for these purposes.
Slides are useful for many reasons (diagrams that need many colors, animations, etc.) and the chalkboard is useful for answering students' questions and giving more examples if needed. I don't think I could teach well without either of them.
It really frustrated me because unlike when a professor writes all of that stuff out on the board, he was able to breeze through the material without pause in barely enough time for anyone to write anything down. I was really frustrated at those lectures because I couldn't find a balance between taking notes and actually paying attention to what he was saying in the lecture.
There are some use cases for slides. A picture or graphic too complex to be drawn on the chalkboard. Animating an example (I've seen Steve Jobs use this to good effect). In my lectures I strive for a minimal slideshow, lots of chalkboard examples, and live demos of example code.
Additionally, having to write out content in longhand slows down the amount of info you can cram into a lecture.
I'm not sure if you meant that as a positive or a negative, but that was the biggest advantage for me when I had chalk board classes. If you can't write down everything you want to say, your students can't either.
With the right font in your PowerPoint, you can have the best of both worlds.
My algorithms professor wrote out the whole outline of the presentation, then would do the whole thing on the board as he went. I loved it.
That said, powerpoints have a very worthwhile benefit in that redistribution is trivial. If you're fortunate enough to be in an Operating Systems course where you're writing an operating system, there's a large amount of stuff where details are very important that can get screwed up when twice-transcribed. Something like a powerpoint is invaluable.
I think the best presenters use both powerpoints (for main ideas) and a (chalk|white)board, for actually working through it.
But, while powerpoint may be a fundamentally weaker medium, I think part of the problem is that a lot of people are simply bad at it. Having an optimal presentation requires a lot of attention to things like pacing, and separating content between the powerpoint itself and the delivery. I get the feeling that a lot of people don't look further than content. Hint: if you print your slides and distribute them as notes, they are not optimal for at least one of those purposes[1].
[1] However, optimal slides printed out with room to take notes during a lecture can often be made into optimal notes by a good student.
First, look at content. When you're delivering a Powerpoint presentation and a great side conversation arises, you are pressured to return to the content of your slides before you divert too far. If you don't, then you've lost your visual medium for interacting with your audience. Granted, sometimes it's better to refocus, but it's arrogant to believe you can always anticipate the best direction a conversation can take ahead of time. Anecdotally, my favorite classroom memories of school involve the teacher abandoning plans for the day because students were passionately interested in a side conversation. I'll note that none of those teachers used Powerpoint slides.
Next, there's form. Most subjects are easily broken down by bulleted lists, but that doesn't mean that it's always the most effective way to transmit information to others. Some Powerpointers are talented enough to genereate lots of high-quality picture-based slides, but they're few and far between. I've met some of these talented few, and they're always clearer on a markerboard, because they are able to dynamically change their diagrams as I ask questions and comment.
I realize Powerpoint works better for some scenarios, but if given the choice, I'll choose the guy with the marker in his hand every day of the week
1. Non-linearity---it's easy to reconfigure the lecture on the fly if I'm chalking it out on the board.
2. Interactivity---I can ask for and actually use examples from the students when working through something, and I can even ask the students to come up and write something on the board when appropriate.
3. Real estate---In a good classroom, I might have seven or eight times the area of chalkboard as I do projector screen, and I don't need to erase anything until it's all full. That makes it much easier to refer back to earlier points. It also gives everything I wrote a "place", and I can refer back to what I had "over there on that board" sometimes two or three classes later, and if I don't need the precise content (just a general reminder), that's often enough to refresh it in students' minds.
4. Editing---Have you ever been in a PP-based lecture where there were some errors in a formula or graph or equation? (It might be better to ask if you've ever been in one without errors...) These are hard to edit out, and if the slides for students to look at later, how often does the prof correct them first? I had a theory class in grad school that was terrible for this.
One "big" advantage for PP isn't even unique to it: sure, I could post a PDF of my slides for students to read later. You know what I do instead? Snap a photo of the chalkboards after each class and post that.
The only reason to use projected slides IMO is when there is a long formula that students don't have to write down (e.g. it's in the book) that I need to point to, or a particular graph or diagram that needs to be precise. For these things, I stick a PDF of the formula or diagram on the course website, and pull that up during class to talk about it... briefly, before going back to the chalkboard.
I was filling in at a community college for one of the techs who was running the distance learning classroom for a biology lecture. The person teaching it had the camera pointed at his face while he went on in a monotone lecture voice with small breaks of drawing on an overhead. Everyone in the classroom fell asleep. When he called us asking for questions, I had to mute our mikes and wake people up. I taped the lecture, but would have hated to watch it again.
What value do you get from a professor reading his slides to you, versus just downloading them and reading them at your leisure? With the professor at the chalkboard, however, you feel like you are getting more of his thought processes with more spontaneity. And more of a feeling that it is OK and encouraged to stop him with questions, and maybe even diverge from the day's planned lecture on occasion.
I wonder if universities with professors standing in front of chalkboards will start to attract the best students over time.
