Johann Sebastian Bach's activities as a teacher appear to have been both widespread and respected. Nevertheless, the substantial body of evidence concerning his teaching and methods is far from complete or authoritative. Furthermore, the circumstances of each individual pupil and Bach's own changing whim apparently led to a variability of approach. As in other areas of his activity, such inconsistency was probably also the result of the composer's continuing quest for improvement and his almost compulsive thirst for new challenges. Bach seems to have been a highly creative teacher, surprisingly so for his historical environment.

There are various ways in which we can identify Bach's pupils:

1. Recorded or preserved written evidence from Bach himself (say in a written testimonial) refers to personal instruction. It may also refer to collaboration in performance under his supervision (which is a rather different matter).

2. Written or reported evidence from an individual pupil may refer to study with Bach, sometimes with further comment concerning when and how the learning process was effected.

3. Sometimes music manuscripts compiled in collaboration with pupils demonstrate an educational purpose; but one needs to be careful here, since there may be many reasons why Bach required copying assistance without any specifically didactic intention.

4. Written reports by third parties, stating that others have been, are, or hope to become students of Bach.

5. The records of choir schools (the register of Thomasschule alumni, published by B. F. Richter in the BJb 1906 and subsequently destroyed, is useful, but it does not cover the Externer (day-pupils), including Bach's own sons).