My instructor was good, he was grade 6 whatever than means.
Grade 6 - A very high standard with no significant instructional weaknesses
Grade 5 - A good overall performance with some minor weaknesses in instructional technique
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Grade 4 - Competent performance with some minor deficiencies in instructional technique
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Grade 3 - Inadequate overall performance with some deficiencies in instructional technique
Grade 2 - A poor overall performance with numerous deficiencies in instructional technique
Grade 1 - Overall standard of instruction extremely poor or dangerous
Grade E - This is a grade 1, 2 or 3 but if you have been teaching for less than 1 year you get given an E (educational) grade and a kick up the backside.
The difference in grades is not an even spread.
Grade 6 and 5. are pretty close. 5 just means you've covered the syllabus correctly but your instructional technique may not be perfect or you may have not mentioned something of a minor nature.
Grade 4. is a lot different to a 5. You'll notice for a grade 4 it says "deficiencies" which is a stronger word than "weaknesses" meaning it's not just that they missed things but there are errors in their methods of teaching.
Grades 3 & 2 are a long way down from a grade 4, and are considered to be below the required standard. Your instructional technique will be poor, you may be missing parts of the syllabus or worse giving incorrect instruction/information.
Grade 1. You will be will have done things such as allowing pupils drive through red lights. Not put on their seat belt, or basically lost control of the lesson/vehicle.
If you have been teaching for less than 1 year. Grades 1-3 are termed Grade E (Educational) You need to seek additional training and you will be re-tested within a few weeks.
All instructors are re-tested periodically. For a grade 6 it may be 3 years between check tests. for a grade 3 it may be less than 12 months. (though they are nearly always running behind)