Well, I'd question whether "poaching" is a bad thing anyway. I don't agree with governments rewarding top performing schools, I agree with schools performing well, hence more parents want their kids to go there. In a controlled market, there will be tendencies to underperform. Of course, there will be exceptions, where there is a team of highly motivated staff that are willing to give a good effort, like Glen Waverly Secondary College, for example. However, we have to look at the lower end of the scale: underperformers like Pakenham H.S. I believe that competition is what will boost education in these areas. Of course, there will still be worse schools, and an "education gap" similar to a "poverty gap" but I'd argue that this is what is an efficient allocation of resources: the services provide for the customer.
I will expand on this point: if you send a poorly educated (I'll argue this is because of not only previous education, but also family influence, cultural upbringing, etc.) kid into a highly competitive private school with strong academic discipline, he/she will most likely not receive the benefit. It is a consumer/supplier mismatch, an inefficiency. However, if you argue that equality must be achieved, then we must concede high quality education for some in exchange mediocrity for all.
The reason why there are the exaggerated inequalities involved with 'liberalised' education is exactly because of the 'moderate' or 'centrist' approach to education. When government gets involved, adverse externalities are created, such as the negative externality involved with teachers cheating with their students. I do not see this happening at all if schools are left alone.
EDIT: The whole thing about "measuring" education is a problem, and it is something that definitely should not be decided by the government. Parents should make that decision for themselves. They may want to foster a love of music and sport rather than just plain academics, and they may send their kid to a school that encourages these activities instead. It's when governments that get in the way, problems begin. That's just my observation.
Another edit: I want to address the issue of equal opportunities, which my second argument seems to neglect. I believe that there is a way out for those who started off on unequal footing, through government loans or private loans (depends how pure of a libertarian you are here). Either that, or some schools may offer scholarships to the disadvantaged because there are benefits of having the prestige of "goodwill" and "kindness" involved. If there is truly potential to be unlocked within children born in low socio-economic circumstances, it will be granted by the free-market.
Also, those types of education you mentioned near the end would be allowed in a free-market society, they are the types of schools that wouldn't be allowed in a "one-size fits all" government controlled education system.