(a) The only valid causes for termination of a contract heretofore or hereafter entered into with a professional employe shall be immorality; incompetency; unsatisfactory teaching performance based on two (2) consecutive ratings of the employe's teaching performance that are to include classroom observations, not less than four (4) months apart, in which the employe's teaching performance is rated as unsatisfactory; intemperance; cruelty; persistent negligence in the performance of duties; wilful neglect of duties; physical or mental disability as documented by competent medical evidence, which after reasonable accommodation of such disability as required by law substantially interferes with the employe's ability to perform the essential functions of his employment; advocation of or participating in un-American or subversive doctrines; conviction of a felony or acceptance of a guilty plea or nolo contendere therefor; persistent and wilful violation of or failure to comply with school laws of this Commonwealth, including official directives and established policy of the board of directors; on the part of the professional employe: Provided, That boards of school directors may terminate the service of any professional employe who has attained to the age of sixty-two except a professional employe who is a member of the old age and survivors insurance system pursuant to the provisions of the act, approved the first day of June, one thousand nine hundred fifty-six (Pamphlet Laws 1973).¹ In such case the board may terminate the service of any such professional employe at the age of sixty-five or at the age at which the employe becomes eligible to receive full benefits under the Federal Social Security Act.²

(b) Nothing within the foregoing enumeration of causes in subsection (a), shall be interpreted to conflict with the retirement of professional employes upon proper evidence of disability, or the election by professional employes to retire during the period of voluntary retirement, or the authority of the board of school directors to require professional employes to retire during said period of voluntary retirement, or the compulsion on the part of professional employes to retire at the attainment of age seventy.