I think they are paid a lot. But the rate should be determined by the market. As a comparison, private school teachers earn about $30k/year.
Teaching is a special vocation since it should regard the truth, which, ultimately, is God.
Socrates opposed the professionalization of teaching since he believed that he who paid the piper would call the tune. He was pretty much right.
The reason is simple: although education (broadly signified) is the parents' and society's highest obligation, (attested to by every philosopher of depth), by nature we neglect the most important things.
To tell the truth liberals have long understood this far better than conservatives. The battle in my opinion is essentially lost both in public and private schools. The only real positive signs seem to be coming from the home school movement. Through parents dissatifaction with formal school, I see some signs of good things, but it may be too little to late.