I remember back in 'A Discovery of Witches', Diana Bishop's progression was basically the opposite of a typical training montage. She's a complete denial case, suppressing her magic because of trauma, and her power kind of... grows on its own when she's not looking, especially when she's emotionally compromised. The real development came from unlearning her fear rather than practicing spells. It felt very organic, like her magic was tied to her personal growth and her relationship with Matthew.
In the Harry Potter universe, the muggle-born witches and wizards who kept their talents hidden before Hogwarts always fascinated me. How did they manage? Petunia Dursley's stories about Lily making things happen accidentally, or young Hermione reading everything she could get her hands on to understand her abilities before getting the letter. Their development was clandestine, self-directed, and fraught with the anxiety of being discovered, which added a different texture to their power.
Comparing that to something like 'The Once and Future Witches' by Alix E. Harrow, where the sisters have to hide their craft in a society that's violently purging witchcraft. Their power development is all about coding it into domestic tasks, into nursery rhymes and sewing patterns. They don't get stronger through traditional study; they get stronger by remembering, by reclaiming the hidden, everyday magic their society tried to erase. The closet is less about personal fear and more about systemic oppression there.
The progression always seems tied to secrecy itself. The magic adapts to be quiet, internal, or disguised. It's rarely about raw power increasing in a straight line; it's about control shifting from involuntary leakage to deliberate, concealed application. That tension between hiding and the innate need to use the ability is where most of the character development happens for me.