A "schoolmaster" (Greek paidagogos) was a person (often a slave) who was delegated as tutor and guardian for young boys until they came of age (usually about 18 years of age). It was a temporary, and not very prestigious, position. When the son entered on all the privileges of adult sonship, the schoolmaster's responsibilities were finished. Paul compares this domestic relationship to the spiritual relationships when Christ replaces the law as the controlling basis of our lives.

Source:

KJV Defenders Study Bible, by Dr. Henry Morris, Ph.D.
Publisher: Thomas Nelson
Language: English
DEF 10 ISBN 0-529-10444-x
DEF 10-1 ISBN 0-529-10445-8