I haven't read Caitlin but this issue comes up quite regularly.
I'd vote 100% for shorter, more frequent holidays. Both my DSs regressed at least one term during the summer hols between reception and year 1 (or DS2 would have done unless, mindful of DS1's experience, I hadn't kept up the daily reading etc during the holiday!). We've now had 4 summer holidays and it's been my experience that 4 weeks would have been ample. By week 5, frankly, they're getting bored and snappy with each other. The novelty has well and truly worn off and it'd be easy to spend, spend, spend your way out of their ennui. THEN, of course, you have to tackle the exhausted 5 year old on a 7 week long half term that is the consequence of long, 'infrequent' holidays.
Below the age of say, 9, a child, (in my opinion!), really has no concept of what 'six weeks' feels like.
How about 2 weeks off at the beginning of June, then August off? Wouldn't that increase the chances of catching some good weather SOMEWHERE along the line?
As a parent, of course I liked having 6 weeks off the routine and the chaos of a school day morning on the days I wasn't working but I sure got tired of those days we had to be out of the house a good hour earlier than a school day to drive the boys half way across counties to childcare arrangements before I got anywhere near MY work! AND the boys frankly got a tad bored with the 28 quid a day each holiday club they were attending. I appreciate I'd have to do the racing around anyway in that I'm not proposing fewer holiday, BUT they'd be broken up throughout the school year and not be the one long 'grind' that they can be now.
A friend of mine has 2x DSs at private prep. She ruefully concludes that the incredible pressure her boys are under during the school term of 8.30-4pm days, an hour's homework, half an hour's music practise etc etc at least prepares them to be just like daddy in the ridiculous hours he works to fund the whole shooting match! How she wishes they had less full-on pressure in their wildly condensed terms and she had less of the 8 weeks she has to 'entertain' them over the summer. But I'm really talking about the state sector as she accepts she's made her choice.
Finally, are we not in the 21st century? The school holidays were built around the seasons of the agricultural and observant Christian year. Could it not now be renegotiated?