105 ILCS 5/34-84.1

By mutual agreement of a teacher and the board of education, the board may, but is not required to, grant the teacher a leave of absence to accept employment in a Department of Defense overseas dependents' school. If such a leave of absence is granted, the teacher may elect, for a period not exceeding the lesser of the period for which he is so employed or 5 years, (a) to preserve his permanent status under this Act, and (b) to continue receipt, on the same basis as if he were teaching in the school system subject to the board of education, of service credit earned for requirements of promotion, incremental increases in salary, leaves of absence and other privileges based on an established period of service or employment. A person employed to replace a teacher making the election provided for in this Section does not acquire permanent status as a teacher under this Article.