Prince George, 6, is “very happy” at his school, where he is simply known as George Cambridge.

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On September 5, 4-year-old Princess Charlotte will start her day just like schoolchildren around the world. She’ll put on her new uniform, zip up her backpack and smile for the camera — her mom Kate Middleton is usually the one taking the pictures — before she heads off for her first day at school.

The outgoing little princess is joining her 6-year-old brother Prince George for the first time at Thomas’s Battersea, a $23,000-per-year private school some three miles from the family’s Kensington Palace Home.

“She can’t wait to be with George at big school,” an insider tells PEOPLE. “She is so excited about it all.”

And with two year of experience there already, George is ready to show his sister the royal ropes.

“They are close in age, and they spend so much time together,” adds the insider. “Playdates [with outsiders] can be tricky, so they learn to lean on each other.

Just a few generations ago, the thought of future kings and queens attending school alongside their subjects was unheard of — Queen Elizabeth was exclusively homeschooled – but the young royal is thriving.

A source previously told PEOPLE that the future monarch is “very happy” at his school, where he is simply known as George Cambridge.

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In addition to core subjects like math, English, science and history, students are taught an era of enrichment classes, including French, computing, drama and ballet. Prince William says George “loves” his ballet classes, which he started taking in Year 1.

Girls and boys each have three standard uniforms: winter, summer and sports, with an additional ballet uniform. All students wear the Thomas’s navy jacket all year long. Navy gloves and scarves are optional – and shoes must be “polishable.”

Kindness is the schools’ key rule. “We expect pupils at Thomas’s to be kind,” the school’s website states, “to be good friends to those around them, always on the lookout for those in need of a word of encouragement or a listening ear.”

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