Don't use slides to teach a class
The other day I attended a course on diagnostic technologies. The subject of the day was the mathematics of test validity. It involved variables such as false positive rate, false negative rate, disease prevalence in the population, number of subjects in a trial, etc. The instructor taught the course with PowerPoint slides.
While there are numerous statistical subtleties in interpreting data, the basic mathematics involves no more than a bit of first year calculus. Nevertheless it was confusing. Unless a student is writing down the mathematics as it is presented, he/she will not absorb it. Slides allow an instructor to present information too quickly. It's hard to absorb the meaning of equations as a passive listener.
In the old days, a science lecture would unfold on the chalk board in a step by step manner. This gave the student time to absorb the material and reinforce the learning process by taking notes as the instructor wrote on the board. There was a deeper connection between speaker and listener.
Slides are great for presenting a broad picture of research that has an interesting narrative. They are a poor way to ingrain mathematics or a scientific theory in a student's head. A slide presentation is better at inspiring interest than it is at teaching methodology.