In Capturing Magic, the second book in the series, Shannon starts attending the Seminary of Magic on Androva. Underage magicians must complete five years of training before they come of age.
In order to enter the Seminary, your force field has to be strong enough for you to write your name in magical energy in the air in front of you, and hold it there for at least one minute.
It's a pretty basic test, but then magical ability usually starts small (unless your name is Shannon Blackwood!). It keeps increasing until the coming of age ceremony, which fixes it forever. A certain event in Androva's history, prior to Stealing Magic, made this restriction a necessary part of Androva's Code.
The Seminary is a large building in the centre of the city. If you were to look down on it from above, you would see that it is constructed in the shape of a large H. Of the six magical disciplines, three are taught on each side. The centre contains the Seminary's own Repository of Records and also places to eat and study.
The building is made out of black stone. The photo shows you how the appearance of that stone can change, depending on whether the magic inside it is visible. Sometimes all it takes is for the sun to be shining directly onto it. Other times you have to be projecting your own force field in order to attract the magical energy from the stone.