Réponse :
The students and the teacher put their right hand on their heart (that show respect), they stand up straight, focus on the american flag and recite the Pledge of Allegiance that is 'I pledge Allegiance to the flag of the United States of America and to the Republic for wich it stands one nation under God indvisible with liberty and justice for all.'
French school don't have any ritual before the class start.
The americans students wear normal clothes in the video, they don' have any uniform, seems like they don't have any particular dress code.
Almost all the French school don't wear any uniform, they still even have dress code like, no short dress or short skirt, no low-cut shirt, do not wear any hat in the class.
J'espère que cela t'aura aidé ;)