DD1 is currently doing a language exchange to France - for three months! She's 15, so a bit older than your DS Sparkling,, but she's also pretty shy, and we also don't have a spare room.
We also don't live in the UK (so it was a French-German exchange rather than French-British), and it's noticable that UK exchanges are both less common and not as long. A week is better than nothing, but it's a taster rather than a way of achieving real fluency.
The key components to success are:
- Your DC really wants to do it (it's not your idea and they're reluctantly going along with it)
- Both families make a real effort to make the guest child feel at home and understand that what may come across as 'sulkiness' might actually be teenage hormones combined with total shyness and difficulties with the language.
In our case, it was DD1's idea all along, and she's had to make a real effort to overcome her shyness, but (maybe as a consequence) we're immensely proud of what she's achieved. She's even in a different school year to her exchange partner (seconde rather than terminale) so she's had to go into a completely strange school group and do all her lessons in French. It's taught her a lot, not just in terms of language skills, but also self-confidence and independence.
Neither family (us and the exchange partner's family) have a spare room. In both cases the host children moved into a bedroom together and enabled the guest child to have a room to herself, which I do think is important. If you're in a 'strange' environment, it's nice to have a zone where you can have some privacy.
Both the girls also made a real effort to get to know each other beforehand, via Facebook. We also mailed with the other mother quite a bit to clear up issues like favourite foods, allergies, extra lessons, who pays for what. We achieved a real parity with what we 'offered' the other child - we took the French girl for two weeks to the Austrian Alps and southern Germany, and DD1 has just spent a week in Paris and a week on the Cote d'Azur (staying with friends rather than luxury hotels etc). I think there would have been a bit of bad feeling if one family had taken their guest on a brill holiday but the other family had done nothing nice or special - and that's about making an effort rather than spending oodles of money.