I realize I'm a couple months late to this topic, but since no one else has replied: in my public school district it's about a $7,000/year difference for the first 5 years or so, with slight incremental increases. These increments grow steadily: after 12 years or so the difference amounts to roughly $10,000/year.
This is, at least in my opinion, a pretty substantial pay scale difference, considering how little money secondary school teachers earn (at least those beginning their careers).