EC is the only one that gives 30 credits..12 lower and 18 upper...I think TESEC gives some (18)?, dont know about Charter Oak..Empire State isnt in the big 3 but I think they give 18 also you will need to check directly with any of the others besides EC as this is just what I recall.

EC gives the 30 credits for a score of 80th percentile or better on any of the GRE Subject Tests...GRE Subject Tests Overview

If you score less than the 80th percentile, then the amount you get is less...roughly it works out to like 3 credits per 5%. Tests are given 3 times a year April,Oct and November and cost $130 bucks.

If you have further questions about the schools, you might want to ask in that forum, for others start a new thread here.

Blitz