The reality would have to be far more complex than we see. I actually do like the show, but I'm also reading between the lines.
Yes, they WOULD take the cases that they have the best chance of helping, plus the cases would be vetted to screen out (and refer on) those who really do need professional help.
PLUS - what we see is probably days and weeks of filming, edited down to one hour. Having been there done that with documentary/news filming, I know just how much film they use, to only screen seconds to maybe a minute, sometimes.
It's very staged - the format is always the same. In the beginning, before the credits, you see Jo Frost, in full "nanny" outfit (glasses, hair in severe bun, black nanny suit) in the London cab watching a DVD of a family, on her laptop. She looks up in horror at the camera and says something like, "Wow! THIS family really needs my help!" and off they go to that address. As if it hadn't already been well set up.
Then she arrives, spends the day observing - in full nanny rig, looking a bit scary - often looking meaningfully, or in horror, at the camera when wither kids or parents do something very wrong or inappropriate (or "unasseptable", as she used to pronounce it).
Next day (at least, we THINK it's the next day) she turns up, looking friendlier with her hair down, no glasses and a plain coloured shirt with trousers. First she sits down with the parents and gives them her analysis. Then her rules are brought in - she explains to the kids what they have to do also and what they can expect if they break the rules. The "naughty chair" or the "naughty mat" or similar. Then we watch as Jo coaches the parents in the process of following through and implementing the rules. Since some of these rules and problem behaviours relate especially to evenings and mealtimes, she HAS to be, in reality, spending several days at least with the family. I've watched episodes which deal particularly with a child who won't go to bed properly; they show progress over a number of nights. They might try to make it look like an instant solution, but if you scrutinise the show 'between the lines' clearly it's not an instant process.
After she leaves the parents to it she often says, "I'll see you in a few weeks". And we then see her watching footage of how the family is coping (or not). She then comes back to fine-tune things (how much longer does this take? Nothing is said) after which the family is apparently doing fine. Then, almost as the credits roll, they deliver a report on how the family is doing, months later. Subtle, but how would they know unless they have continued to work with them?
You've got to think - what is the purpose of SuperNanny, from the point of view of the show's producers? Why do they make the show?
My thoughts are that it's to show a range of problem behaviours that some parents have to deal with, along with a professional's point of view on how to best deal with it and reduce the problems. The problem behaviours are not just the kids, they're also the parents. Sometimes the parents are just not organised enough (perhaps a mum trying to work at home, perhaps made worse by a dad's unrealistic expectations of how much his wife can manage and still look after the kids properly as well). Sometimes it's a child who is more demanding than the average parent can handle, but a change in technique is all that's needed. Who knows? Because we only see the edited, sanitized, cut-down version, designed to showcase the scope os assistance available when you call in a professional nanny (or similar).
Something I've also seen in watching this show - they are careful to NOT say that ALL children can be easily 'cured' by a day with SuperNanny. I remember one episode in particular, where she urged the parents to get their son assessed for possible learning disorder/Asperger's. But from what I've seen, I suspect that is rare, that such a family would make it to air.
I have seen a few cases where she comes back again, even later. Problems have continued and she's made her "follow up in a few weeks" visit more than once.
What we're shown seems simplistic. I suspect what actually happens is far more complex. They're not going to invest the time and effort they DO invest (plus the cost of production) to have a family fall apart the moment she walks out the door after two days. It would give her a bad name; it would give the show a dud reputation. And they can't afford that - she's doing commercial endorsements now (which I think is selling out, frankly). She'd never get the commercial jobs if she had no professional credibility, so behind the scenes they must be doing SOMETHING right.
Like a lot of 'reality' shows like this, where people's genuine problems are solved within half an hour or an hour of prime-time, it is far more complex and takes a lot longer than it's commercially acceptable to let on.
It must be wonderful for those families whose kids only need a tweak from SuperNanny. But for most of us on this site - I suspect we'd never get past their screening process!
Still, it's nice to dream, and live vicariously...
Marg