Circle Centre mall -- with its food court arcade and ample shopping opportunities -- can at times be a hub of activity for the 46,000 blue-jacketed teens who cluster Downtown during the national FFA convention. [...] it was there, on a third-floor perch near an escalator, that Phillip Caler, a 16-year-old student from a small Texas ranch town, went over the side and fell Thursday, striking a railing on the second level and tumbling downward before coming to a rest on the hard tile floor 41 feet below.