What makes a great teacher? It is a question that has been pondered for generations, and the proliferation of titles in use - including advanced skills, post-threshold and excellent teachers - reflects the difficulty of finding an answer.
Now a Government-commissioned committee undertaking a review of teaching standards has become the latest body to attempt to solve the problem.
The working title it has come up with - master teacher - may sound more akin to a medieval guild, but it reflects an ambition to uncover the magic ingredients shared by leading exponents of the profession. "It's the teacher you remember, the teacher whose subject you loved because of the way they taught it to you," review chair Sally Coates told TES. "Teachers are all different. It's very difficult to describe it absolutely, but we've tried to capture some of the qualities of a master teacher."
The qualities of master teachers, which are listed in a draft document published today, are undeniably abstract.
To qualify for the title their pupils' outcomes must be "outstanding", although the document stops short of recommending a floor target. They must be analysed in the context of school, national and international standards, it insists. "I don't want the context to be used as an excuse, but I think the context should be taken into account," said Ms Coates, principal of Burlington Danes Academy in west London.
As well as displaying a "deep and extensive" knowledge of their subject, a master teacher should "command the classroom" and display "consistently outstanding and motivating, often inspiring" teaching. There should be a "stimulating culture of scholarship alongside a sense of mutual respect" in lessons, and they should share their expertise with colleagues and immerse themselves in extra-curricular activities, the draft guidelines say.
Ms Coates hopes the new standard will raise the bar higher than previous efforts. Post-threshold status, she argues, is viewed as little more than a pay progression, and advanced skills teacher status is usually seen as a job role, rather than a set of standards.
The excellent teacher status is rarely used. When it was introduced in 2006, Labour ministers predicted 5,000 teachers would apply in its first year; in reality, just 34 did. Master teacher status, Ms Coates argues, is "much simpler and clearer", designed to inspire teachers to hone their craft. "Everyone can aspire to it, but I don't think everyone can attain it," she said.
The review's remit does not cover whether the other advanced teaching titles will be phased out, and the final decision on whether to implement its findings will be taken by education secretary Michael Gove after the consultation ends on 11 November.
"If I were a younger teacher, I would have loved to have got this status," Ms Coates said. But with the details of how it will be assessed - not to mention implemented in pay scales - yet to be finalised, doubts remain whether other teachers will agree.