I did much the same as Ewfflyer mentioned earlier. I would charge for what I figured we did in ground (.3 or .4 typically), but I'd knock it off for longer flights if we didn't spend significant time reviewing something.

On the flip side, I had some instrument students prepping for IFR cross countries I hit for two hours of ground when I was helping them go through the planning and what not.

The important thing is to make sure the student thinks it's worth it. If you're one of those instructors who hits them for .3 ground every flight while you sit in your office playing Angry Birds while they preflight, they're going to get sick of it eventually.

Speaking of, I always went outside during the preflight, even with commercial and CFI level students unless I had something else to do. I wouldn't talk to them or follow them or anything, but I'd be outside so a) if something came up, I'd be there to ask, and b) as soon as he/she was done preflighting, we could hop in the plane and go. No reason to waste their time or mine.

Charge for ground if your actually teaching something (or flight planning etc). You should charge for this and the student will expect to be charged for this. However, charging ground time just for walking out to the airplane, or just bs'ing with the student is a no-no in my book. My $0.02.

Well, what about the time when you are responsible for the student's safety? IE: On the ramp, supervising preflight and walking to and from the aircraft? Does something "come up" every time? No, but things have definitely come up and I've had to intervene, for safety or other reasons. Are you saying that you do not charge while the student is effectively flying the aircraft and you do not have to provide instruction? You are paying for a service, this is how it works in the real world. At least you don't have to pay for the entire activity up-front and then "whatever happens, happens" (like weather cuts it short, etc).

Yes, just "BSing" is not acceptable as far as charging and honestly, you shouldn't be doing this much with students (little is ok and you need to develop trust/working relationship obviously), but they shouldn't be your best friend. Please don't take this to mean that an instructor and student can't have a conversation or meal. If an instructor is charging for this though there is probably more wrong than just the fact that they are over-charging, they are probably not professional and worthy of the rate when they are "teaching". Even when I was "strict" as far as how I charged the time the students were still getting a helluva deal. Not paying for preflight, usually not paying the entire "with the instructor doing something constructive" (IE: not eating obviously) on XCs, not paying for paperwork, scheduling, etc.

Realize that in direct business sense, you are paying for this person's time and expertise. The instructor needs to do what they need to do to provide safety and oversight. There is more than just showing up after preflight and hopping in the aircraft. There is sometimes scheduling, paperwork, and all sorts of extras (this is why you are paying them for their time, not just when you are in the plane with the engine running with them).

For those that think it's not fair to get charged for the time the instructor is providing oversight, safety and supervision, I don't know what to say, except this is the real world and you have to deal with it sooner or later. Instructors should be providing the best possible instruction that they can, and if you feel they are not doing that, let them know, and find a new one if you need, but please don't try to turn it into a charity either. Aviation is not cheap and upholding decent working-rules is not being mean or trying to be unfair. It's just the real world. Students and instructors should realize that it should be a professional service.