A movable partition system includes a movable partition, a floating jamb attached to an end of the movable partition and located within a pocket configured to retain the movable partition when in a retracted position, at least two base plates attached to the floating jamb, and at least two jamb stops attached to opposing interior walls of the pocket. Each of the at least two jamb stops are configured to engage a respective base plate of the floating jamb, wherein the floating jamb, the at least two base plates, and the at least two jamb stops are configured such that disengaging the floating jamb from a secure position within the pocket when the movable partition is in an extended position requires disengaging one of the at least two jamb stops from the respective base plate on each side of the movable partition. Methods of providing a security barrier are disclosed.