Here is the final word:
"Exchange visits lasting less than 28 days, where overseas parents accept the responsibility for the selection of the host family, should be regarded as private arrangements and will not require registration" (DCSF)
Interesting.... Now, correct me if I 'm wrong, but this is very carefully worded, isn't it?
I would read it as follows: if we ask our French/German/Spanish colleagues to ask their parents to say they accept responsibility for the selection of British host families, then our parents will not have to register with ISA. Would they be willing to say that we are doing it on their behalf?
However, if the foreign parents are not willing to do this and say, with justification, that we, the British teachers, are responsible for the selection of the host families, then it is no longer a private arrangement and British parents will have to register with the ISA. Geddit?
So, essentially, this is what we thought it was all along. Only if it is a private arrangement can we avoid asking our parents to register.
In theory, we could send our students' forms to our colleagues who could ask their parents to choose a family, then it is a private arrangement, as they have taken responsibility for the choice.
Oh dear! This is a pitiful-sounding compromise (which may not be a compromise) and I think that, ultimately, I would be likely to ask my parents to register.