我出國唸書之前,在碩士班時曾經在補習班兼任GRE老師,履歷表上是這樣寫:Part-Time Teacher for a GRE Tutor School.
如果是代課性質的兼任老師,也可以說是Supply Teacher或 Substitute Teacher。(http://hk.dictionary.yahoo.com/search.html?s=supply+teacher)
至於實習老師,Training Teacher 或 Practice Teacher 或 Teacher in Training都可以。