On an intellectual level, I understand the extrinsic motivation of both the teacher and the hiring school. She saw an opportunity to "trade up" to a more exclusive, high profile academic environment (and probably more money); the school, in the words of their administration, was "desperate" and needed to fill the position; and our school, faculty, and especially students were just "collateral damage".
As with most mainstream independent schools, this particular school belongs to a number of professional organizations. Their three principal affiliations make the following demands on their members. The first says: the school shall practice ethically in the areas of employment, admissions, [and] recruitment (students and staff); the second requires that: the school practices ethically and within the law in the areas of employment, admissions, [and] recruitment (students and staff) (not sure who copied from whom in this case!); and, the third states that: the school ensures that it is aware of any employment-related, binding contractual obligations of the candidate; and the school carefully avoids inducing or assisting in a breach of those contractual obligations.
So having sworn these oaths of ethical practice, how does a school spin violating them without a second thought? To be honest, on a purely practical level, I totally understand how a Head rationalizes making this kind of decision. Let's face it, her or his job is to recruit, develop and retain the best faculty and staff possible. Heads have an obligation to their students, parents and ultimately the Board to ensure that the programme is, and remains, the highest calibre possible. When being asked around the Board table, "why is our Math programme the pits?", the answer - "I was bound by Principles of Good Practice not to hire the best person I could." - demonstrates a strong sense of ethics and probably a weak sense for professional survival! At the end of the day, Heads will usually put the health of their own school ahead of the niceties of professional collaboration with their colleagues in other institutions.
That's the practical side. But what about our role to build and nurture an "ethical community" within our four walls? We expect our teams and coaches to observe the highest standards of good sportsmanship and fair play; we severely discipline incidents of plagiarism or cheating on tests; and, we trumpet our commitment to community service and environmental stewardship. We preach ethics to our students - we should practice ethics in our operations. Sometimes doing the right thing will cost us in the short term, but ultimately it is never a bad decision.
So, practically, what can a Head do when faced with this ethical conundrum? To begin with, you ask permission to immediately contact the current school to ascertain their contract status. If the candidate refuses permission, you politely thank them and remove them from consideration. If they say yes (which they should if they are the kind of staff member that you are looking for), you find out whether or not their current school will let them out of their contract. Why waste time pursuing someone who is not really available? There is an obvious downside for the candidate (their hand has been exposed to both schools) but that is really not your problem! If their current school gives you the green light (another warning sign!) then you can feel free to proceed with the process. No matter what the outcome, you have taken the high road.
Finally, when you are thinking of recruiting staff in the late summer, always remember the apocryphal story of the elusive Peter Kitchen. One summer, he was hired to teach French, given an advance for travel from the UK to Canada and then subsequently didn't show up in September. What makes this an even more cautionary tale, is that there were actually three Canadian independent schools that were expecting him to be on their faculty that Fall. As for PK? He collected his advances and continued his quiet teaching career somewhere in the Midlands. As far as I know, he is still in the market for a job across the Atlantic - but I don't think that I will be looking to him to replace the teacher I just lost!