You will love these expository prompts because they are already in STAAR format for 4th grade. Keep in mind that 4th grade prompts for STAAR need to be specific to a person, place, event, or idea that the student like or loves. If you are looking for prompts more appropriate for middle school and high school, here is the link you can copy and paste to find those in my store.
The only thing I would like to remind STAAR Teachers about regarding the main idea on the prompt page is that 4th grade refers to it as the central idea, 7th grade uses the term controlling idea, while 9th grade utilizes the phrase thesis statement, and 10th grade a position statement. The prompts for middle school and high school need to have the key words, Write about the importance of something, OR Write about whether or not one thing affects or impacts another in order to be in STAAR Format.
For expository in Texas, you only need to explain what you think, feel, or believe with examples. For persuasive, you have to try and get the reader to see things the way you do and exhort or call him to some sort of action.