You're right Chad, I had to look for the definition of "GPA" ! (for the record :
here)
Your understanding of the French system seems accurate. To enter
grandes écoles you might need a certain
mention at the baccalauréat : mention "assez bien" (>12/20), "bien" (>14/20), "très bien" (>16/20) ; and "passable" > 10/20, means you passed
However, from Bongbang's original sentence
(my parents promise to buy me a bike), I rather thought the person speaking was a child.
If that is so, I think the most likely to be heard in France in an equivalent situation, would be "si j'ai des bonnes notes", or stronger : "
si je n'ai que des bonnes notes" - of course, it's more subjective, since it all depends on what marks the parents judge "good" or "not good"...
PS: mais si, c'est possible d'avoir 20/20 !! (dictée, en 6è
)