The department of retirement systems shall credit at least one-half service credit month for each month of each school year, as defined by *RCW
28A.150.040, from October 1, 1977, through December 31, 1986, to a member of the teachers' retirement system plan 2 who was employed by an employer, as defined by RCW
41.32.010, under a contract for half-time employment as determined by the department for such school year and from whose compensation contributions were paid by the employee or picked up by the employer. Any withdrawn contributions shall be restored under **RCW
41.32.500(1) or
41.50.165 prior to crediting any service.