Community college educator Dr Biden has continued to teach alongside her role as First Lady, while the early years has been a huge focus for the Duchess throughout her royal career.
There was much excitement from pupils at Connor Downs Academy as Kate and Jill arrived at their joint engagement.
The Duchess was also asked about the most recent addition to the royal family by a member of the US media - the Duke and Duchess of Sussex's daughter, Lilibet Diana Mountbatten-Windsor, who was born on 4 June.
"I wish her all the very best. I can't wait to meet her," replied Kate. "We haven't met yet. I hope that will be soon."
Kate and Mrs Biden were taken to see the rabbits – Storm, Wampa and Cindy – and the first lady went armed with a bowl of large carrots and stood alongside Kate, chatting over a gate to Mr Masters and four pupils with Storm.
Later today, the Duchess will join Her Majesty and the Duchess Cornwall at an event in celebration of The Big Lunch at the Eden Project.
The three royal ladies will also attend the G7 Leaders reception at the eco-visitor attraction, alongside the Prince of Wales and Duke of Cambridge.
Afterwards, Prince Charles will host a reception for the G7 Leaders and CEOs from the world’s largest companies to discuss how the private sector can work with governments to tackle the climate emergency. Prince William will also join his father.
The Duchess and Dr Biden then led a roundtable discussion with a number of representatives from the early years sector who have helped influence Kate's efforts to create a national conversation that gives every child in Britain a better start.
Kate and the US First Lady share a passion for improving early years development and displayed their own informal transatlantic alliance on education during the visit.
The Duchess told Mrs Biden: "I'm committed to this for a long time. I hope our two countries can continue on this and share data."
Next week, Kate will step up her work in this area, with a major announcement outlining how she will elevate the importance of early childhood and continue the conversation on this vital issue.