This is important information for hostelers too.
Germany has about 600 official HI hostels - "DJH" is the acronym for the German hostel association. Website: www.jugendherberge.de/en/
These are some of the best hostels on the planet - lots of investment has poured into these places over the last 20 years or so, and many are now like hotels, IKEA style; others are housed in castles and other fortifications, and they're nicely appointed too. Low-priced family packages with meals are common in winter. They are generally great places to stay for individuals, couples, and groups.
The only problem is that this investment in hostel infrastructure is possible only because of heavy use by German schools; a week-long outing during the school year with your class and teacher is routine for most children. But that means that during instruction periods, the hostels are chuck full of rowdy pre-teens that will make your hair stand on end if you're older than 17. School outings are particularly abundant in fall, spring, and early summer when the weather is more agreeable
So if you plan on hosteling, it's wise to plan your stay DURING school break periods, when the kiddies are at home. German hostels in late July and August when almost all schools are out are a particularly good option.