Some schools in Northern Ireland already allow girls to have a choice between trousers and skirts.
Enniskillen Integrated Primary were prompted to change their policy after Rhea and Astrid contacted Dr Mairead Ryan, whose research outlined a relation between school uniforms and physical activity.
In a letter to the school, Dr Ryan said: "Gendered uniforms can limit girls' movement and engagement in physical activities."
"Uniform items like dresses and skirts can restrict certain movements and inhibit young girls from climbing, jumping, and participating in other forms of active play that are crucial for their development," she added.