Stubborn can be a compliment. Obstinate never is.
Both words describe someone who will not change their mind, and most children use them as though they are interchangeable. In a comprehension paper that costs half a mark.
The difference is sympathy. Stubborn determination wins races; a stubborn refusal to give up is the sort of thing a school report praises. Obstinate is the same trait with the sympathy taken out — it is what you call it when the refusing has stopped being admirable.
A useful test: you can imagine a character being described as stubborn by someone who likes them. Obstinate is almost always the narrator taking a side.
Refusing to change your mind, even when you might be wrong.
Similar: obstinate, headstrong, defiant
Refusing to change your mind or do what others want, however hard they try.
Similar: stubborn, headstrong, wilful
Comprehension questions often ask how the writer wants you to feel about a character. If a passage calls someone obstinate and a child reads it as a neutral word for determined, they have missed the writer's opinion — which is usually exactly what the question was testing.
Definitions and example sentences on this page are the ones a child sees inside Wordrealm, taken from our list of over 1,100 words. It is free to browse, with nothing to sign up for.
Plain-English guides to each test, from the councils’ own pages: Kent Test · Medway Test · Bucks Secondary Transfer Test