Princess Aiko, the only child of Crown Prince Naruhito and Crown Princess Masako, turned 12 years old Sunday.

The princess, in the sixth grade at Gakushuin Primary School in Tokyo, has started studying history, which she enjoys doing with her father, who has a detailed knowledge of Japanese medieval history, according to the Imperial Household Agency.

A video released by the agency showed Princess Aiko creating presentation materials with her father for a history class assignment.

The princess acted as a group leader during a school trip to historic sites in Nara Prefecture in June.

She also completed a 500-meter swim in Numazu, Shizuoka Prefecture, in July.

When younger, the princess sometimes had a hard time attending school. But she has not missed classes in the past year, except when sick, the agency said.