IT teacher speaking here..
My own education was unusual, and that's probably why it sucked a little less than most people's experiences. I was kicked out of school when I was 12 and spent the time learning to program (I'd already got some experience typing listings from magazines into my old Amstrad cpc464 and sworn at syntax errors). I was making full games in GFA Basic and STOS fairly quickly on my Atari ST. Returning to the school system I was bored shitless.
I'm now a poacher-turned-gamekeeper. I went abroad to teach, and had a decent amount of freedom with what I could teach, until the school introduced GCSEs for our older students. The practical stuff (MS Office, jeez) was stuff my 4th graders could do.
My 4th graders (age 9/10) could use MS Office, do some basic floor-turtle programming, basic DTP using advanced (non-microsoft) software, open up a PC, take it apart and put it back together and were comfortable in Adobe Fireworks and Photoshop. My 7th graders were comfortable with web design. My 8th graders had a working knowledge of databases (not just MS Access) and how one could use them in a variety of situations. My 9th and 10th graders could packet-sniff, program in PHP, etc. Then came GCSEs and we all got bored to tears. The practical was too easy and the theory was too dry, outdated and pointless (not to mention every lesson we'd have to run through corrections for the mistakes in our Cambridge-uni-produced books).
Unfortunately, the problem I suspect is one that exists on many levels:
1. It's hard to recruit skilled people on teaching salary. I'm unusual, I actually enjoy teaching, and yet my background means I can program many different languages, do web design, take PCs apart, do penetration testing, etc. Not too many of those people want to teach. Most of the time kids can outsmart their IT teachers and that really doesn't inspire confidence.
2. Kids have very short attention spans now compared to years ago. They want facebook, farmville and porn. They don't want to have to think too hard. They want quick and easy. Too many years focusing on making stuff accessible has, I suspect, created a generation that can't cope without hand-holding. Games didn't have tutorials on how to scroll the screen with your mouse when I was a kid.
3. Parents don't value education. Not all parents of course, but many British parents just want their kids to fit in, rather than being successful. The parents who say "oi Tyrone ya f*ckin c*nt get ere naaaaah" tend not to want their kids to be too swotty. Computing, like maths and science, is swotty and so not something to be encouraged. We need to change this culture.
4. The curriculum is shit. I mean seriously shit. When I got hold of a recent GCSE IT past paper I just laughed at it, as my primary kids could handle it. It was designed by idiots.
5. As alluded to by others, CLAIT is useless. Teach it at primary maybe to make sure the basic skills are there, just as we teach spelling, addition, subtraction, etc at that age, but move on quickly to real computer science.
I consider teaching to be a lot of fun and a very rewarding career (not financially, but on an emotional level) and if done well it could be a good career choice for many IT professionals. The only problem of course is that IT pros typically lack the people skills that teaching requires, and that's another facet of the problem. It's a subject where expert knowledge and teaching skill very rarely combine, due to the fact that the subject and teaching require two very different personality types.
IT education in the UK is a mess. I just hope that it can be sorted out at some point before all IT work ends up being outsourced to India not because it's cheap but because the skills just don't exist in the UK.
I'm sure there was something else I wanted to put here but I think I've gone on long enough!