Harry greeted a crowd of delighted pupils from St Vincent's Catholic Primary School in Acton and was introduced to the school's pooch Winnie, according to The Sun.
WATCH: Harry makes friends with a frisky puppy
The Duke helped students plant saplings in the school's garden area and also planted his own tree in honour of the QCC and Woodland Trust which has provided 74,000 trees across the UK.
Harry went solo for his afternoon outing, leaving heavily pregnant Meghan Markle to rest as she continues her sabbatical from royal engagements in the lead up to the birth of Baby Sussex.
The couple were photographed on March 19 paying their respects to the victims of the Christchurch mosque attack at New Zealand House in London.
The young royals were also spotted last Saturday leaving the christening of Lena Elizabeth Tindall, the youngest daughter of Harry's cousin Zara and her rugby player husband Mike Tindall.
The Duchess of Sussex is expected to give birth at some time in April, and bookmakers are running even odds that the baby will be a girl.
Harry and Meghan's arrival will be the eighth great-grandchild for Her Majesty Queen Elizabeth.
Strong contenders for the little one's name include Alexandra, Alice and Grace for a girl and Albert and Alexander for a boy.