Is instructor contact with a student's steering wheel widely taught? I've heard some instructors say that they practice this technique quite frequently. Personally I've never had an instructor even ask to steer my car, much less suddenly grab the wheel in a slide.

It would totally freak me out if someone grabbed my steering wheel as I was trying to concentrate to steer out of a potential spin, most likely resulting in a crash that could have been avoided if I am left alone to correct the car myself.

What's the SOP as far as club training programs are concerned for instructor intervention?

If you spend hours with a student on track, and they still wont use the whole thing,
I'll ask if I can help! But I would NEVER grab the wheel if I thought we are on the
edge of a spin. You can only tell them to track-out so much.
The reason this probably has not happened to you is you get it, some don't and need assistance.
The SOP is "in a spin, both feet in"

If a student by all means doesn't get the point of any associated exercise then it's time to re-think the strategy and perhaps take a different approach or go back to the drawing board.
Physical intervention like moving the steering wheel or trying to control any elements of the car is IMHO not appropriate and could lead to devastating results.
What happens if the student gets into a similar daily driving situation by himself w/o an instructor riding shotgun - then what?

Only practice, more practice and lots of seat time may help to achieve a goal, but there is no guaranty that the student will ever get there, some talents may be required.

The development of "psychomotor skills" to react on sometimes contra-intuitive motions can not be thought by jerking the steering wheel, it must be learned and experienced in a controlled environment - slowly.
Only when the instructor works with patience and time to observe a student very closely while using analytical skills from a comprehensive pool of knowledge and own experience then there is a good chance of being successful. The result of the analyzes should determine exactly the training program and step by step instruction/goals for the student.
That means putting him/her into a situation in a controlled and safe environment like a skid pad an old airstrip for example.

And what most people seem to forget: for anything you do in life - Speed is a by-product and will only be achieved through practice and developing excellent skills.

So the only thing I'd physically move in your car is clicking in the seatbelt ;-)

if a student is having difficulty with a particular turn or turn in point i will ask them if i can gently assist them by placing my hand on the wheel through that turn....most of my students have had no issues with it....for example, my student at ra last year was having an issue with turn 3, he wasn't waiting long enough, once i showed him what i wanted him to do it was a non-issue....if a student says no that's fine also, i'll try something else

turn 6 at Miller, which is about 160 degree, right hand, decreasing radius turn. Car in front of me was going off about 2/3 of the way through the turn. I observed the car straighten out, go off track in a controlled manner, and come to a stop well off the track surface (lots of run off room). Thought the driver had done a good job at controlling it.

Found out later the instructor had reached over to straighten out the wheel to prevent a potential spin.

This was an ACNA event btw.

That's exactly my point, what would he have done w/o the instructor?
If you can't make a turn then most likely because the car is going too fast; so instead of being forced to intervene during the incident perhaps an earlier intervention like "slow down!" would have helped to avoid the entire scenario.....just a thought ;-)

Now he has a little more edgy and slight nervous student on his hands who may have lost some confidence, not a good scenario IMHO because it could have been avoided, don't you think?

the concern there is to keep everyone and their cars safe. So the student had a set back, so long as they improved the rest of the day it was all for the better.

I have touched a wheel once...I dont plan to ever do it in the future.

Not a good technique but I've had to do it when they just couldn't keep the wheel still through corners. You have to warn them before you do it so they don't freak out!

But as Steve said, not something you will do often.

On the other hand, I've heard of it being done when cars were out of control and students are frozen. Just haven't experienced that yet and hope I never do!

In general, I'm not at all a fan of doing that, and I think in non-emergency situations, you have to be able to verbally communicate what you want the student to do.

a friend of mine, though, was instructing a guy in a saleen mustang (don't like stereotypes, but in this case...) at Lime Rock. Seemed totally normal in the pre-grid, conversations, etc; first 2-3 laps were totally fine; the guy drove the line reasonably well.

4th lap, on the straight after exiting the downhill, the guy eyes were locked on the dashboard. The instructor tried to get him to talk... braking point came; instructor says "brake." Still looking down, no braking. "BRAKE!"

The student, still looking down at the dashboard, finally spoke: "140!"

Fortunately, Lime Rock has a long straight runoff at the end of the main straight. My friend, knowing there was no way the were making the corner, grabbed the wheel to keep it pointing straight and said "we're going straight."

Where he blew thru the chicane before turn #1 at Thunderhill doing about 135..and I look down and see I have pulled up on the emergency brake. Needless to say..we had a lil chat in the hot pits after that.

... knowing a thing about them. If I got into a novice's car, and it was something like a Vette, I would impose an immediate limitation on max speed. I had an instructor do that to me once (he was doing a check ride to sign me off) and it was VERY annoying; but I respect the reasoning behind it.

Now I've got a track car that can't go fast enough to scare anyone!

I cant see ever putting my hands on the students wheel when the fit is hitting the shan.
First off you do not have all of the control input so how do you properly correct something when the throttle or brake are doing something else out of your control.

2nd I would not want that kind of liability. YOU are responsable at the point when your hand touches the wheel. Granted you are trying to possibly save your own life but if things really go south than you might be on the hook. Putting yourself in ownership of the car is something I would take a hard look at.

That said I have "driven" the line with my hand lightly touching the wheel with a student at reletively slow speeds. 5/10's or less.