hollingburst you're right it's so easy to have a knee jerk reaction to boarding (at what ever age) but few parents are callous and uncaring nearly all consider boarding with lots of concerns, they think very carefully about what they're doing and monitor their child's happiness and development very carefully. Many for what ever reason believe that boarding is the best option for their child.
I agree with this, children who have a special talent, children whose parents travel extensively, children whose home life is stressed etc could all benefiit from boarding school, maybe in some extreme circumstances even as young as 8.
But is is very hard to come up with any scenario in which it is better for an 8 year old to be in a different country to his parents when they live - presumably happily - year-round in a place known for its excellent schools and vibrant culture and community.
In fact the only reason given by the OP is that it was part of their strategy for him to attend Eton or some similar school. I find that very hard to fathom- it isn't necessary to go to boarding prep in order to get into a good school in the UK and so many posters have said.
And it is even more bewildering because the OP is american herself. There is no such thing as an elementary boarding school in the US. The earliest they start is middle school which is about age 11/12- and even then that is incredibly rare to the point most people wouldn't even know they exist - you'd have to google it. hand on heart I cannot think of one american woman I know who would have considered this for more than a nano-second.
This is actually a very strange situation-it is like OP and her husband managed to transport themselves back 100 years with regard to schooling. I feel like I'm reading a virago or persephone novel from the 1920s where the mother doesn't want her son to go to boarding school at 8 but the father says "all the men in our family do, it'll make a man of him"