Excellent resources from Bruce, and Dave Herren is right on point with his comment about test scores being only one part of the story. If possible I suggest you visit, or at least call the schools you are interested in, so you can ask questions and get more information to help with your decision.
From a general perspective, most of the North Fulton Schools are so good acedemicaly, that you almost can't make a bad decision there - but there are differences and some may be better suited to your families needs and preferences.
Case in point - where I live in Roswell (East Cobb) many folks seek out homes in Walton High, and academically it is one of the best 2-3 schools in GA - but, some parents may feel that it is too agressive with its standards and and may put their child under excess pressure if they are not a steller performer - other parents like the specal programs where kids can excell. But if you chose Lassiter where my son goes, or Pope, you certainly would not be making a mistake - they are all three excellent and in the top ten best in the state, and nationally ranked.
I definitely would not listen to any agents personal opinions regarding what is the best school - or best neighborhood for that matter - that is too subjective and its a personal decision you should make based on a little research and what is right for you.
For actual test scores and demographics go here: http://www.doe.k12.ga.us/Pages/Report-Card.aspx
or here: http://gosa.georgia.gov/report-card
Some third party sites can be useful, but you have to be careful. One site agents often recommend is Great Schools - I personally don't care for that site because it tabulates "parents opinions" into the rating which can be very misleading, and I feel it is a conflict of interest. Reviews are fine for restaurants, but schools should be rated by their students test scores and graduation rates. I have seen plenty of parents on Great Schools giving glowing references to thier childrens very poor schools right here in metro Atlanta.
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