Ron and Neville's Magical Transformation

Fan theory: Ron and Neville's lack of magical ability in the Harry Potter series can be attributed to their wands. In the wizarding world, it's essential to win a wand's allegiance for it to perform at its best. Ron initially uses his brother's old wand, which doesn't suit him. For much of his early years at Hogwarts, he struggles with his magic, often leading to misfires and mistakes. However, once he acquires a wand that chooses him, his magical abilities significantly improve. He becomes on par with Harry in terms of magical prowess, especially in Defense Against the Dark Arts.

Neville Longbottom has a similar experience. He starts with his father's wand, which doesn't align with his magical essence. This results in a reputation for being poor at magic throughout the series. But when his father's wand breaks during a confrontation at the Ministry of Magic, he gets a new wand. With this wand, Neville excels in herbology, leads a rebellion, and eventually becomes a professor. Although there are some exceptions in their earlier years, this theory suggests that the change in wands is a pivotal factor in their improved magical abilities, aligning with the idea of a wand choosing its wizard in the Harry Potter universe.

While this theory has its limitations and may not cover all aspects of Ron and Neville's development, it offers a plausible explanation for their early struggles with magic, and how obtaining wands that match their personalities and abilities made them more accomplished wizards in the later books.