As noted in Wikipedia:
The Thomanerchor (English: St. Thomas Choir of Leipzig) is a boys’ choir in Leipzig, Germany. The choir was founded in 1212. At present, the choir consists of 92 boys from 9 to 18 years of age. The members, called Thomaner, live in a boarding school, the Thomasalumnat, and attend Thomasschule zu Leipzig, a Gymnasium school with a linguistic profile and a focus on musical education. The younger members attend 76. Grundschule in der Manetstraße primary school. Johann Sebastian Bach served as director of the choir from 1723 to 1750.
Here are a few videos of the choir: