Honestly, I think the search for good 'Matilda' fanfiction with real character growth is a lot trickier than it seems. The book is so complete and perfect on its own that most fan writers just retell the story with a few extra scenes, which doesn’t do much for development. The ones that stick with me are the ones that ask 'what next?' or 'what if?', pushing the characters beyond the final page of Dahl's story.
There’s this one older fic I keep going back to, I wish I could remember the title, that followed Miss Honey navigating her newfound independence. It wasn’t about grand adventures, but about the quiet, messy process of becoming your own person after a lifetime of fear. It showed her making mistakes with money, feeling guilty for small pleasures, and slowly learning to trust her own authority beyond just being Matilda’s advocate. That felt like real growth, because it was uncomfortable and slow. For Matilda, the best fics often explore the cost of her genius—social isolation, the burden of being the 'adult' in the room, or her power manifesting in less controlled ways as she hits puberty. A really unsettling but brilliant one had her accidentally reading the chaotic, fleeting thoughts of everyone around her as a teenager, forcing her to develop emotional filters and empathy, not just intellectual ones.
The crossovers can be surprisingly good for this, too. I read a 'Matilda'/'A Series of Unfortunate Events' crossover where she and the Baudelaires were in a sort of gifted-kids support group. Watching Matilda, who’s used to outsmarting one vile adult, try to apply logic to the systemic, absurd cruelty of Count Olaf’s world forced a different kind of maturation. She had to learn that cleverness isn’t always a shield, and sometimes you just have to survive together. That’s the kind of growth I look for—not just more of the same victories, but explorations of their flaws and new challenges that their original story didn’t have space for. The Trunchbull’s defeat was an ending, but it was really just the beginning of their problems, and the fics that get that are the keepers.