@Heather **************
, just so you're clear how an ED visa works.
You enroll, pay the tuition, get documentation from the school and apply for a 90 day single entry ED visa from a thai consulate. <- that's where you're gonna have a problem given your prior entry history :O
However for the sake of arguement lets say you DO get the 90 day ED visa. You get stamped into the country for 90 days and when that 90 days runs out you get documentation from the school go to the thai immigration office and apply for a 90 day extension. You would do that the whole year (if it's a year class).