- Stephen Fry - Headmaster Barnes (voice)
- Alan Turkington - Mr Lange
- Isabel Adomakoh-Young - Miss Greenwood
- Livia Nelson - Young Tara
- Emilie Largier - Madame Martin
- Tabitha Byron - Tiny Girl 2
- Ella Maisy Purvis - Girl 1
- Sebastian Croft - Ben Hope
- Araloyin Oshunremi - Otis Smith
- Fisayo Akinade - Mr Ajayi
- Chetna Pandya - Coach Singh
- Olivia Colman - Sarah Nelson
- Georgina Rich - Jane Spring
- Joseph Balderrama - Julio Spring
- David Thackeray - French Teacher
- Bradley Riches - James McEwan
- Bradley Riches - Student 3
- Irina Leoncio - Spanish Teacher
- Jack Barton - David Nelson
- Phoenix Stone - Older Student
- LJ Bennion - Ticket Clerk
- Benjamin Cléry - Ice Cream Server
- Sam Firth - Young Charlie
- Eden Gough - Young Tao
- Euros Lyn - Security Guard
- Thibault de Montalembert - Stéphane Nelson
- Ethan Joseph-Robert - Alex the Artist
- Rebecca Root - Principal Edwards
- Rachael Stirling - Amanda Olsson
- Habib Nasib Nader - Richard Argent
- Annette Badland - Ivy Olsson
- Hayley Atwell - Aunt Diane
- Eddie Marsan - Geoff Young
- Martin Marquez - Ant Spring
- Darragh Hand - Michael Holden
- Malcolm Rennie - Grandad Roger
- Tamara Ustinov - Grandma Nancy
- Jonathan Bailey - Jack Maddox
- Christopher Hatherall - Uncle Rich
- Lucy Speed - Susan Denvers
- Lara Decaro - Clara Spring
- Georgina Bitmead - Esther Spring
- Amber James - Producer
- Catherine Bailey - Katy Newnham
- Nkara Stephenson - Kent Tour Guide
- Elliot Douglas - Leeds Tour Guide
- Alex John MacLean
- Brett Thomas
- Euros Lyn
- Hugo Nicholson
- Daniel Edwards
- Paul Young
- Jamie Laurenson
- Hakan Kousetta
- Dylan Rees
- Zorana Piggott
- Sebastian Dale
- Taz Fairbanks
- Michael Griggs
- Adiescar Chase
- Keith Tunney
- Alistair Bolt
Joe Locke interpreta a Charlie Spring en la serie.
Kit Connor interpreta a Nick Nelson en la serie.
William Gao interpreta a Tao Xu en la serie.
Yasmin Finney hace el papel de Elle Argent.
Tobie Donovan interpreta a Isaac Henderson en la serie.
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