Alfred asks about teachers and the language changes.
There tends to be three sources for computer science teachers.
One group tends to be like me -- refugees from industry. I've met some who admitted they weren't competent to work in the industry, and others like me who don't like the atmosphere.
One group are math teachers. Some of them have choosen to teach computer science -- they decided they wanted to teach an elective. Some were choosen by someone else, maybe because they had a few programming courses on their transcripts.
Then there is one last group. I run into them for time to time. An uneducated administrator thinks that anyone can teach CS, and picks a business teacher, or a science teacher. Again, some had had a programming class on their transcript. Quite a few of them haven't. I also won't express too much of an opinion about the last group except express my sympathy. I too have been thrown into teaching something I wasn't prepared to teach.
Notice I haven't mentioned anything about the certified / alternative certification battle.
But the issue is why does the language change drive teachers out of computer science. Some of the people who couldn't cope with the language changes were CS people. Some of them were math people.
I'm lucky, I had a really good education in computer science and was even lucky enough to take a course surveying computer languages. I also wrote the same software in several different languages when I was working in industry as we needed a common set of user interfaces on different hardware. I doubt that I am the normal. Throughout my career, I've met people who could only program in one programming language, or maybe only two or three. I do know that it took a major shift in thinking from going to Pascal to C++. It also took a major shift in thinking when going to C++ to Java. Things are done differently. It takes a good bit of writing code and making it work to make the shift.
So why did teachers quit over the language change?
First, I don't think many quit over going from Pascal to C++. The ones I know that quit, when they heard about them ove to Java. When we moved from Pascal to C++ we had to throw everything out. I know I threw trashcans of handouts and materials away. Not the first year, but the SECOND year, because nothing I had from Pascal worked. And it wasn't just books and written materials, it was IDEAS! There were few assigments that survived porting from Pascal to C++.
So a lot of people anticipated that happening again. And they didn't want to go through that a second time.
Second, they received zero support on moving from Pascal to C++. I know, I taught one of those workshops. I got no support from the College Board. And in fact, the only thing that saved me, was a) new textbook adoption that happened at the same time, and b) a local cheap college where I could take C++ at night. And I didn't even know I needed to do that until November or so. I was even lucker that I had a good professor teaching the class that would take the time after class to help me with teaching ideas. The gas money and the tuition money came out of MY pocket.
So if I had been at retirement again when Java was announced I might well have quit to. Just the anticipation of change and no support is enough to do it.