(1) Part-time certificated employees shall become permanent certificated employees based upon the following formula:
(a) For certificated employees employed four-fifths time or more, each such year of employment shall count as a full successive school year; and
(b) For certificated employees employed one-half time or more but less than four-fifths time, each such year of employment shall be credited against the three-year requirement for acquiring permanent certificated employee status in an amount proportionate to the term of such employment for each year. Such certificated employees shall become eligible for permanent certificated status at the beginning of the school year next succeeding the year in which they attain the proportionate amount of time.
(2) Any certificated employee who achieves permanent certificated employee status shall not lose such permanent certificated employee status because of reduction in force resulting in a contract amendment which would reduce such certificated employee to any part-time employment position.