It's interesting that of those who report sucess in French education with their offspring, it appears to me that most have girls. My son was failed by french education despite starting at the age of 3 and staying with it until age 9, came out as Idun reports, with very low self esteem and almost apologises his existance at times. He was an outgoing and frankly cocky toddler but 6 years in France changed him. He experienced racism from teachers and other boys (note always boys) and generally found the rote learning and silent classes boring.
So do girl fair better I wonder, as girls tend to rally around, perhaps even mother those that are different?
For the OP I think 14 is too late to change schools, he's about to make choices at GCSE, do you really think he can be as successful in a foreign language and take serious life changing exams in just a couple of years.