Pass out four sticky notes to each student. During their sustained silent reading or library time, have them locate an example of each of the four types of sentences and write them on the sticky notes -- one on each note. Put pieces of butcher paper on the walls of the classroom, each with a different sentence type written at the top of it. Have the students put their sticky notes on the appropriate sheets of butcher paper. Challenge them to check each sheet for any errors.
Adding a dash of creativity to a grammar lesson will help keep students engaged. Have students work together in groups of four to write a play with four characters. The catch is that each character can speak in only one type of sentence. For younger students, you can assign a play genre, such as mystery, which is good for creating interrogative sentences. The genre also allows older students to be creative. The play can be about 20 lines, and the groups can present their play to the entire class. This lesson idea comes from "Awesome Hands-on Activities for Teaching Grammar," by Susan Van Zile.
Instead of having students simply take notes on the types of sentences, help them make their own reference book using a regular 8 1/2" by 11" sheet of paper. There are several ways to make a book from a sheet of paper, so choose a method that suits the age group of your students. For instance, you may want younger kids to just fold their sheet in half, while older students can create a mini book that requires making eight folds. Allow students to design a cover and write the type of sentence, a definition and an example on the inside page(s).
Creating advertisements can be a fun, creative activity. Show students examples of ads that use a variety of sentence types. Choose a product, or have the students choose their own product, and have them write an ad that uses all four sentence types. This activity works particularly well when it's coupled with a unit on persuasive writing or the media.