Start this activity by giving your students a list of regular verbs in present tense, past tense and past particle. After describing how regular verbs typically end in "-ed," give them a list of sentences in the present tense with the verb circled to ensure they know which word it is in the sentence. Have them rewrite each sentence in the past tense, showing them the "-ed" rule in practice. Next, do the same exercise with irregular verbs, giving them a list containing regular verb sentences and irregular verb sentences mixed together. The exercise will help them distinguish between the two by the specific word and context of the sentence.
Once your third-graders understand the difference between regular and irregular verbs, hand them a worksheet you wrote yourself containing the improper use of irregular verbs. Treat them like regular verbs and write, for example, "Now that we've beginned to understand irregular verbs, read through the following paragraphs. After you've readed them, correct the verbs I've writed incorrectly by figuring out the proper past tense form for these irregular verbs." Continue in this style and leave spacing after each misspelled and misused verb for your students to write the proper tense. Consider also giving a list of the solutions for the students to choose from if they have yet to fully grasp the irregular verb concept.
Give your students a list of irregular verbs with three columns: one for present, one for past and one for past participle. For example, the row across could read "Fight," "Fought" and "Fought." In the following rows, eliminate one of the tenses at random and have the students figure out and fill in the proper version of the irregular verb. Once they grasp the idea, you can make the exercise more difficult by giving them only one of the three tenses.
After the third-graders complete the "Fill in the Blank" activity, this is a natural next step. It follows the same concept but uses sentences to frame the irregular verbs, helping students better understand the context of each irregular verb. Something similar to "The movie I saw last weekend _____ very funny. There ____ a few jokes I didn't get, but I bet it was funnier than the sequel will ____. I went home to ____ dinner and, after I ____, I started to ___ my favorite book. After I ____ the first chapter, I went on a bike ___ with my friend and we _____ faster than I've ever _____ before." Not only will this exercise further cement the different tense forms of irregular verbs, but it will help students learn to use irregular verbs in sentences.