Genuinely don't know whether AIBU here. Please be gentle
DS2 (10, Y5) is an absolute dream at school. Teachers consistently say he's clever, helpful, responsible, tries hard, friendly, polite etc etc. Attainment levels are good.
DS1 (12, Y7) is clever but his reports this year have consistently said that he mucks about in lessons. He's had lots of detentions, keeps kicking footballs around in class 
and across most subjects he didn't meet his (high-ish) end of year targets. He's explicitly admitted to me that in some subjects he doesn't put effort in at all - subjects that I consider important, like English and French. We've had LOTS of conversations about this over this academic year and he knows I expect more from him on the effort front. However he's v good at maths - mostly I think without really having to try very hard - and got Level 7a for the end of Y7 which I know is great. He's also done well in science and history. So a mixed bag - but it's his attitude I'm worried about.
I bought DS2 a jacket he'd been after (£50) to reward him for being lovely and trying hard in school. Since reception, no teacher has had a bad word to say about him.
I congratulated DS1 on the maths and good levels in a couple of other subjects, but said I wanted him to try harder in other core subjects.
I didn't rub DS1's face in it but DS2 has told him about the jacket. (I didn't tell him he shouldn't.)
DS1 now saying I'm BU and unfair not to reward him for his good results in maths.
AIBU? (Or was I just being a twat to reward DS2)
V sorry if this looks like stealth boasting - I am proud of DS1's maths ability but tbh more worried that he's getting into a pattern of thinking he doesn't have to try at things. He's convinced that a talent for maths will turn him into Bill Gates 
while I worry he's going to underachieve horribly. I may be being a tad neurotic.