What phrase is used to call attention when a dignitary enters the classroom?

The phrase used to call attention when a dignitary enters the classroom is "Attention on deck!" This phrase is a formal command that instructs those present to stand in a respectful posture that signifies alertness and readiness. It emphasizes recognition and respect for the authority and position of the dignitary entering the space. The use of this phrase helps create an atmosphere of discipline and acknowledges the presence of someone of importance.

Other commands listed, while useful in their contexts, do not specifically pertain to addressing dignitaries. For instance, "Stand at ease" is used to ease the posture of those at attention once the dignitary has arrived. "Fall in" typically pertains to assembling troops or personnel for roll call or formation. "Present arms," on the other hand, is a command that instructs individuals to render honors, usually used in conjunction with a salute, often for military ceremonies and flag presentations rather than simply to acknowledge an entrance in a classroom setting.