I was invited to contribute an article of 500 words to a special issue of Scientific American. I assumed that most of the other articles would be unalloyed cheerleading for the wonders of technology. So I decided to talk about both the promise and the perils of technology.

I have seen teachers doing amazing things with the Internet. I have gone to conferences where thousands of teachers were learning how to use technology creatively. I know that technology, in the hands of inspiring teachers, can bring learning to life and empower students to self-direct their studies.

But it is in my nature to look at questions from all angles. That is what is known as critical thinking.

So I wrote about three ways in which technology may be a danger to education.

First is the for-profit online charter school, which provides a poor substitute for real education but is quite…