Another option is to center all objects in the parent container, but the parent container must also set width or percentWidth. When width is not specified, a container or Label will size to fit the content only, so there is no concept of centering.
var _sln:Label = new Label(); _sln.text = _uofsModel.tempLessonTestResults.aUofS[i]; _bgs.setStyle("horizontalAlign", "center"); _bgs.width = 800; _bgs.addElement(_sln);