All school employees not required to hold a certificate, diploma, or credentials to practice in a professional capacity who had previously elected not to be included in the retirement system pursuant to section 79-910 may, after January 1, 1978, and prior to July 1, 1978, file with the retirement board an election to be included in the membership of the retirement system, but such employees shall be treated as new employees and no service credit shall be granted for the years the employees elected out of the retirement system.