Hi,
You mean market rate for gr 2 lessons for home visits? it is about 140 to 180 depending on teacher's qualification.
Actually there are different types of diplomas - Teaching and Performing.
In Teaching diploma, for ABRSM, there is a viva voce section where 2 examiners will ask questions on how to teach different technique or different grades etc. All about how to teach etc.
For trinity, there will be a paper on this as well.
However for performing diploma, it is like other graded exams - 3/4 pieces to prepare and perform (depending which exam board)
Hence, teachers with teaching diplomas and considered 'know how to teach, as they passed the exam already.
However, there are also teachers who can teach well but does not take teaching diploma etc.
Normally teachers will higher qualifications will charge higher.
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Hope this helps