Sight reading is an advanced, specialized skill that is needed in situations such as accompanying.
I don't completely agree with that. I think at the base level, sight-reading is what even 6 year olds do when they are looking at a new piece of music for the first time. If they have good note reading skills up to that point and clearly understand the rhythm; and are fairly strong in the hands, they can look at a new song, play through; yes, there might be a little mishap - a wrong note or two, a note that's not held for the full length, but overall they are looking at the piece and reading it 'at sight' at a reasonable tempo.
To me, sight-reading is playing without relying on muscle memory or aural memory, and seeing the musical notation for the first time, without any previous preparation.
Think about it. When you started learning pieces/songs (like Twinkle, twinkle), it might have taken you a couple of days (20 mins a day) to learn each song... but as we get more advanced, we find that it will take us weeks and sometimes months to learn new material... Why is that? I'd like to think that at this point in time, I have excellent note-reading skills, and a moderate amount of technical skill (compared to the greats), and I can play fairly well without looking at the keyboard, but over time I wasn't regularly taught and assessed on these abilities, and I feel that had I been, maybe my sight-reading could have been much better.
I'd add an extra thing to consider when teaching - fingering principles. Sightreading requires that you be able to come up with an execution that works on the fly.
Maybe, but I think part of that comes from keeping your eyes on the music and reading ahead. I think the less time spent looking at the keyboard allows you to maintain focus on the piano and to read ahead. Plus, sometimes you'll get basic fingering put on the score, so it's simply a matter of keeping your eyes on the fingering as well. It's a good point though, so I'll noodle over that...
You play at tempo, skip notes if you have to etc.
I hate to say but again, I disagree. Yes, it may be handy to skip notes when you're sight-reading for a performance and it is the first time, but I'd like to think that the ability to read everything on the page, and to play everything on the page can be taught or developed. I think part of the skipping notes, may be that your note reading skills are just a little lacking, or the technical development needs more work. Yes, everyone does it, but I'd rather address the problem and try and better myself than just accepting that skipping notes is necessary.
I think these are "necessary but not sufficient" conditions.
2) gives the beginner the most trouble and of course 3) limits almost all of us.
In learning to sight read, focusing on those three will not hurt you. But sightreading is a complicated combination of a number of related skills.
Do you feel there are any other skills that would help sight-reading other than the 3 I initially mentioned? I'm curious to know...
I did not look at the material, because you have to join some kind of site to do so.
No you don't... You just download the file - no signing up or anything, no need to give an e-mail or password. But having said that, I also did forget that you can just attach PDF's to posts, so I'll update that in a second.