Goose I'm sorry, I'm just not surprised by what you say at all, regarding some fitters just not being very good at it.
Is it asking too much that if a fitter 'fails' their training, or doesn't 'get it' after having the training, that they aren't allowed to fit children's shoes?
After all, that's exactly the thing that Clarks is selling their shoes on - that other shoes won't be fitted as well as theirs. A lot of parents feel guilt tripped into buying Clarks on this basis and here you are admitting that some of the fitters are just rubbish at it!
I don't think that's good at all.
We have always had teenaged fitters in Clarks. Their experience can't be more than a year or two.
One pair as I said had got a hole in the toe within a week - the front bit of rubber came off on the first day he wore them to school, and of course there was nothing to protect the obviously poor quality leather after that.
Thankfully I had got them in the sale but still, £20 wasn't cheap enough to throw away.
Another time I bought ds2 a pair in advance, so not fitted, and when I came to try them on him a few months later, they wouldn't actually go on his feet.
Bear in mind that he was in a Clarks 6 and a half at the time - these were a 7 and a half - when I took them, and him, into the shop, they tried them and said, yes, these are the wrong size - they gave us another pair the same size that DID fit 
Their explanation was that the shoes arrived like that, not uniformly sized, some were bigger than others, though they were marked the same.
I couldn't BELIEVE what she was saying. I have only bought very cheap sale shoes from there ever since. We get their feet properly measured and fitted by the older woman at our independant shop now and buy start rite - which funnily enough seem to be made from proper, dyed through, (not just on the surface) decent quality leather.
Many, many times I've had them measured in Clarks and been told they are a certain size, then they have brought out other width fittings or sizes saying 'well every shoe is different and we didn't have anything in their actual size'.
Enough already! What is the point of that? It's a gimmick and a bit of a con.