The various methods all work, and I find students understand navigation better if they think of the track as a "time line" rather than just a direction. This helps to prevent them from quickly being convinced they are where they think they might be, (vague) rather than where they actually are. (definate)The time line will tell you, and when you check position go "what time is it (clock) what should I see at this time (map) and am I there(ground)?"
To make the mental arithmetic easier I teach ten minute marks working backwards from the destination - the ten times table is easier than the six times table when it comes to mental arithmetic. Any odd minutes are at the start of the leg while climbing etc. You then have a prompt every ten minutes to do your FREDA checks and prepare for the next ten minutes workload, particularly when inbound to the destination, and a "sub" ETA which will tell you if your groundspeed is different to that calculated on the ground. And hopefully will never be more than ten minutes off track!
If everything is in minutes, ETA, fuel log etc you have one common denominator rather than trying to grapple with minutes, litres and miles.
Students who do their prep diligently have few problems, especially if they "walk through" the exercise before flying it. One of my instructors chalks it out in front of the hangar, and they literally pace through it, it works very well most of the time - until someone comes along and parks a plane on top of your "destination"!!
The most common part of navigation that people seem to find hard, and which lets them down in flight test, is planning the descent and entry to an uncontrolled airfield. Circuit joining errors are the most common reason I have to fail candidates for PPL. These skills need to be developed early on and any problems ironed out by the third navex before they go solo and develop bad habits. Another thing is that although they have used the wind in planning, lack of awareness in wind direction on a forced landing is the second most common error. Draw a big wind arrow on your map!
Also in the "lost" procedure they need to be able to grasp how far they could have gone since the last fix, like a "keyhole" on the map. some have real problems with this and again ten minute marks help.
Sadly there are some who will never have a sense of direction - I had one who was convinced that East was North and that a couple of large features had moved overnight,
but with patience they can get there in the nd!