At times, when you're an ALT looking over the months until the next school vacation period, the thought of all the lesson plans you're going to have to come up with before the break can be quite daunting. But (for high school ALTs, at least) when you break the year down into the terms, the number of regular uninterrupted teaching weeks can turn out to be quite low.
Case in point - the first term started around the 9th of April, and will end around the 20th of July. At the start of the school year there are various ceremonies and necessities to be taken care of that disrupt the schedule, including class photographs and health check-ups. Then there's often short school trips - first years go camping in what is called in Japanese the "nature experience" trip. The end of April/start of May brings Golden Week, a series of national holidays grouped together, and a couple of weeks after that come the mid-term tests. Each subject tests the students on what little they had a chance to learn in the brief time when they actually had lessons since the start of term.
I find it faintly ridiculous. At one school I've seen the students at most four times each, and at the other only three. Right before the mid-terms the teachers start to panic about the marks the students will get, and often cancel team-teaching classes with me so they can finish the textbook pages or do revision. The onus seems to be on the teachers, rather than the students themselves, to ensure success in the test. That should give you an idea about the Japanese sense of responsibility, and why customer service is so good in this country. And so yesterday I had two classes cancelled (tests start next Friday, folks!) and today, similarly. This means I now have no classes today. None. Whatsoever. And it's only 10am. This would be a good time to catch up on my correspondence.