You are technically correct but we are talking about students who have gone astray. Besides I did not want to make my post too long.If a student has got himself/herself lost I doubt that they could accurately calculate a reciprical course.
Map reading should start by the time the aircraft has reached altitude. It is important to map read from this point on because trying to work out where you are half an hour down the track becomes very difficult.
Not only should a line be drawn on a map the timing along that line should also be noted. On take-off, note the time on the map or start a stop watch and that will show where you planned to be at any given time of your journey. It is essential to look ahead on the map so that you can say to yourself I will over fly a road running from 10 oclock to 4 oclock in 1 min or whatever.
If you are not where you planned to be something is wrong. Either your flying accuracy, flight planning, heading or speed flown, or wind used in flight planning is wrong. An experienced flyer should be able to determine which element is the cause. I would not expect a student to be able to work it out in the air. A guess is not good enough so turn round and fly home.
A reciprical of the course flown will get the student near enough for the to departure field to be recognised. If he can remember the drift factor and can apply it in the correct sense then by all means use it but if there is any doubt, don't go there.
If a student gets lost after passing a way point he should return to that way point so that he then knows where he is. Now he can decide whether to set out again on the original planned flight course or fly the reciprical of the course flown to that way point thus returning to the departure field.
I have no idea what instructors are teaching these days but the above is what I would teach.
In addition to the above, making a radio call as soon as a pilot decides he is lost could help if anyone has equipment to read a bearing on the tranmission - but that is another story.
I can recall in my early days of flying, a low level navex that I went on I steered 030 instead of 003. The flight was conducted at 200 feet above terrain at an airspeed of 360 knots IAS. All of a sudden I crossed a rail line that was not on the map. On checking the obvious elements where an error could be made I soon was able to work out where I was and set a heading to intercept my original course.
Also, map reading is possible over most terrains. I have map read my way across the Nullabor Plains.
