The best way to introduce a new grammar point (especially with high school students) is to draw upon pre-existing knowledge. Numerous studies show that this makes retaining information easier. One great way to accomplish this is with colored pencils.
Identify Subjects and Objects:
To begin the unit, extract several sentences from the target unit by writing them on the board. Identify subjects and objects in simple active sentences using two different colors. Ask students to underline subjects in red and objects in blue. Clearly label each with its function in the sentence.
Find the Verb:
Once this is completed, ask students to use a third color to underline the verb. Again, a moment or two should be spent on reviewing what a verb is. In addition, since the passive form depends upon the active verb form, students should be able to identify the tense used in the active sentence.
Switch the Colors:
Tell students to switch the colors by moving the objects to the beginning of the sentence and the subjects to the end. Ask students to notice how the verb stays in the same position but it changes by using two small steps: adding be before it and changing the verb to its past participle form. Several examples of the previously written sentences can be completed. Students should complete the rest on their own.
Close the activity:
Take time to explain and highlight why each of these forms is used. Ask students to review the sentences one by one in order to point out how the focus of the sentences change when their form is changed.