I don't really know whether I should count the weeks I missed or what. I'm not even very motivated to ponder the question very hard. Which sums up my approach to teaching over the last few weeks. I've been doing it long enough (I'm about to end my 13th year), and I'm not much of a planner anyway, so I can sorta wing it without much thought. I mean, I'm engaged and energetic in class, and I'm getting my grading done in a respectable amount of time. And I have a long-term view of what they're learning. Etc., etc., etc. But my heart's not in it like it usually is. I don't think the kids can tell explicitly, and any increase in probability that I'll get off-topic could easily be attributed to the approach of the end of the year (5 weeks of classes plus finals), but my enthusiasm is definitely lower.
Part of it is the drudgery of the several students who have been coming to class unprepared and signing up to meet with me, and then not showing up. They will not fare well in my end-of-year comments. One of them signed up to show up before school tomorrow morning. So I'll go in 15 minutes early. 15 minutes that I could be sleeping or playing with my daughter. I'd say the odds are 70/30 against him actually showing up. Speaking of sleeping, that's what I notice most about my life now: I'm typically pretty tired at night, but it's hard to go to sleep and give up on quite/alone time and spending time with my wife watching Jon Stewart (whom I think is more comically brilliant) and Stephen Colbert (whom my wife does). So I've been tired a lot. Very tired. No time for naps, really—the post-teaching, pre-dinner period used to be for grading or resting or napping. Now it's for relieving my wife of child care on some days, hanging out as a family on some days, or cleaning up the kitchen to make dinner, or doing some other necessary work that my wife would have done had she not been home with the baby all day (she teaches full-time at a university, but that doesn't require her presence on campus every day). So no naps. I still do a few of my evening hobbies (rehearsing with my musical group, training in martial arts, et. al.), but considerably less often, and for less time, because I frequently take the baby so my wife can get some work done.
I knew, of course, that my priorities would change. And I don't resent or regret the baby in any way (really, I don't—I make the sacrifices willingly even as I recognize them as sacrifices). But I think I feel a little guilty about my students. While I'm less invested in them than some teachers are (I'm not capable of the emotional stamina required), I have, in the past anyway, felt much more responsibility to them than I do right now. Part of the problem, I think, is that I started the year without a child, and now I feel like I'm abandoning my current students a little bit. If I don't connect as closely next year, maybe I won't feel the same guilt. And eventually, my daughter will be in school and have more of a life of her own, and she'll be more attached to us; at that point, maybe it will be easier to reclaim some of my emotional energy for my students.
When I first came back from China with my daughter, Foxy asked the excellent question in a comment of a post about how I might change my approach to teaching now that I have a child. I didn't answer him (I think it's a 'him'...let me know if I'm wrong) because I didn't know the answer yet. We'll consider this post the start of an answer.