The governing board of any school district may grant any classified employee a leave of absence not to exceed one year for the purpose of permitting study by the employee or for the purpose of retraining the employee to meet changing conditions within the district.

The governing board may provide that such a leave of absence shall be taken in separate six-month periods or in any other appropriate periods, rather than for a continuous one-year period; provided, that the separate periods of leave of absence shall be commenced and completed within a three-year period. Any period of service by the individual intervening between the authorized separate periods shall comprise a part of the service required for a subsequent leave of absence for study or retraining purposes.

In school districts operating under the merit system, such leaves of absence shall be granted in accordance with rules established by the personnel commission.