This is the worksheet I designed and used for teaching different tenses in passive voice. I found my students making mistakes in transforming the verb forms because in passive structures we should work on 2 verbs - the main verb of the active sentence which is p.p in passive sentence, and "to be" verb which is the essential part of the passive forms and it turns to different forms in different tenses.The most probable mistake happens in perfect tenses which students mix up using the p.p forms of the main verb and also "be" simultaneously. Here we go,I separated passive verbs into 2 parts in this table : "to be" and "p.p of the main verb" , by this students get to know that every part needs its own care. Take a look and good luck. ;-)