Ok, so you've developed your skills in seeing the errors your learner makes by active instruction and by pro-actively looking for the faults before they happen. Now what?
Well, your task now is to decide exactly why the error was committed. You can only give the correct remedial action if you analyse the fault to discover what caused it in the first place.
In a many instances, on your part 3, a full and prolonged analysis is simply not required
For example, if your phase 1 learner drops a wing mirror check, you could often deal with this with a quick prompt . . .
"Kevin, you know you shouldn't forget to check the interior mirror as well as the offside door mirror before you signal. Why is it unsafe to miss these mirror checks? . . . etc"
You've effectively informed the SE that you've spotted the error, analysed it - it happened because your learner forgot - and you've supplied the correct remedial action, all in one sentence. At phase 1, when your learner is very near to the beginning of their driving course, the errors are usually due to a lack of co-ordination or forgetting procedures.
Of course, the task is not always so easy. What if the same fault is repeated, over and over? In the example above, it could be that your learner never knew about the need for a mirror check at that time. This is unlikely though, as you'd have checked their knowledge of ms-psl before getting the car moving, would you not? Is your knowledge of ms-psl as good as it could be?
In other circumstances, with a more experienced learner, a longer analysis may be required. In fact, you may have to enlist your learners help to find out why the fault occurred.
For example, a phase 2 learner continually cuts the corner on a right turn into a junction. You point out the error and need to offer the pill to cure it (remedial action), but which pill will you give them?
Different pills cure different ills. You don't take a cold remedy for a broken arm, so make sure you analyse why the fault happened before you decide what to do about it.
The first thing to consider, is do you have to pull up or keep moving? In this instance, you'd probably need to pull the learner over in a safe place, to discuss the fault and what you will do about it.
Now, think about the possible reasons for the fault . . . approaching too quickly, approaching too slowly, lack of judgment, not being aware of the road markings, lack of steering control, lack of confidence in clutch control, wrong gear selected, looking at the car controls instead of the road, failing to carry out effective observations . . . need I go on?
There are many causes, and your job is to find out which one is relevant.
In this case, the only option you have is to as a few targeted questions . . .
"Marie, we've cut the corner on these right turns a couple of times now. Can you think why that could be? . . . do you know the dangers of cutting the corner and why we mustn't do it? . . .etc"
If Marie tells you that she didn't know she'd cut the corner, then you'd need to explain what you meant and what the correct procedure is. If she agrees that she'd cut the corner, then point out the possible reasons and ask her why it happened. In many, many cases, you'll get to the root of the problem very quickly. If Marie can't say why it happened, then you'd need to take control and decide which cause is the most likely reason for the fault, and work with Marie to rectify it.
The point to make is, that having worked hard to see the fault, you have to consider all the circumstances to decide why it happened in the first place. To offer the correct remedial action, you need to know what it is that you're trying to remedy.
Start to think now about all of the different areas of driving, and the likely faults that learners commit. Your trainer will demonstrate many of them to you. Consider how you'll actively look for those faults, and also consider why those faults may happen.
Practice the core competencies with your trainer until you can handle just about any situation thrown at you. Considering how varied driving actually is, it's no wonder that you need to have the flexibility to deal with anything. Practicing the pre set tests over and over is almost always a waste of time, because every lesson, even with the same learner, can present new challenges.