Work or Work?

There have been a few posts here lately about time management and the challenges of dual careers. I thought I would take the opportunity to weigh in on my own frustrations.
Like so many writers, I have to keep that full time job to pay the bills. It's not only the money, it's the health benefits that must be considered. I have children so that means large expensives in health care, education and FOOD. So I fit my writing in around working and all the responsibilities that go with being a parent.
I'm luckier than some writers in that my 'day job' is in education. I'm assured of having every weekend off and holidays. After Monday, I'll have the summer months off except for a few days of inservice training. (Must schools switch their grading systems every few years?) Looking at all these days off, one would think I get a lot of writing done in the summer months, but I don't.
It's not having the children at home. They're all teenagers or older, but I wish I could blame it on them. Yes, I'll spend many evenings going to their baseball and softball games. I'll work out with my daughter on her summer conditioning for field hockey, but I do all that during the school year. It's the daytime hours that escape me.
I spent this morning mowing the grass after days of rain. The weeds look like some kind of alien flora invasion into my flowerbeds. I have three stacks of branches and trimmings I need to send through the chipper.... You get the idea. I have plans for stripping wall paper and painting inside for these weeks of 'leisure.'
Even with all that, why do I get less writing done in the summer than during the months I'm teaching? I'm not sure, but I think it's because I spend the days under the illusion that I have so much free time, I can write 'later' after I finish this one more flower bed, clean this one more room or try this one new recipe. At the end of the day, I'm tired, feel fulfilled by my accomplishments and just know I'll have more time to write tomorrow. After all, I do have over two months off.
What about you? Is there a time of year when your writing output is the best? Is there a time when it's the least? And does it make sense that it should be that way?