The phrase permanent employment is frequently the cause of many misinterpretations of tenure legislation. Customary practice is to grant permanent tenure after an individual has served a probationary period. Permanent tenure, however, does not necessarily mean that the local board of education has no authority to make changes affecting persons who have gained tenure status. It does not mean, for example, that the board, so long as its actions are not arbitrary and capricious, cannot transfer a teacher from one school to another. Tenure of employment and tenure of assignment are not necessarily synonymous.