I just spent 5 days at the youth hostel in Lenggries with 67 10th graders. The hostel is super clean and newly renovated. The staff are amazingly friendly and accommodating. The food that we booked was excellent for a hostel, the spaetzel to die for! Breakfast was hearty with plenty for everyone. Vegetarian, lactose free and gluten free dishes were offered.
The only drawback is that the building is very loud, that means that every closing door sounds like a slamming door over the whole building. So if you end up sharing this hostel with a school class, it could be nerve shattering. I know that our pupils who were opening and closing their doors kept me awake all night! So double check that there won't be large groups of kids there!
The beds aren't super comfortable, but it is a hostel so we can't be too picky.
The banks of the Isar are a 5 minute walk away and the town has many cute shops and dining possibilities, including at least one Biergarten. The houses in the village are full of Bavarian charm. A larger town, Bad Tölz is nearby if you need some town charm.More