A person who is employed at least half-time in the public employees' defined contribution retirement plan (AS 39.35.700 - 39.35.990) during the same period that the person is employed at least half-time in a position in the teachers' defined contribution retirement plan (AS 14.25.310 - 14.25.590) shall receive credited service under each plan for half-time employment. However, the amount of credited service a person receives under the public employees' defined contribution retirement plan during a school year may not exceed the amount necessary, when added to the amount of credited service earned during the school year under the teachers' defined contribution retirement plan, to equal one year of credited service.