GRADE 6 DRIVING INSTRUCTOR:

Every driving instructor in the UK must undergo periodic tests of continued ability to give instruction, (Check Tests), in order to examine their teaching ability and to remove sub-standard instructors from the register.
These Check Tests are carried out by the Driving Standards Agency using highly trained senior Examiners. The examiner sits in on an actual lesson and grades the instructor on a scale running between 1 to 6, dependent on their teaching ability.
To remain on the Driving Instructor Register instructors must achieve a

BASIC MINIMUM STANDARD OF GRADE 4.

If they grade lower than 4 three times consecutively then they are removed from the register.
The grading scale is listed below.

GRADE 4 is adequate.

GRADE 5 is good with only minor deficiences.

GRADE 6 is very good, the highest standard with no significant weaknesses.

The DSA grading system is the ONLY official indicator of a driving instructor's ability, you may see instructors advertised as five star, professional, fully qualified etc etc,
However, according to the DSA's own figures the majority of instructors in the UK are graded at the basic minimum standard of grade 4.

Below is a copy of my last Check Test Grading sheet.