This is an older 4th grade STAAR benchmark exam, but it is still a great resource for the price!. It is aligned to the 2013 Release and even has the correct proportional number of Readiness/Supporting standards. There are 48 questions and an answer key included.
I have 2016-2017 aligned questions on my website, and it's free. http://www.lesstestprep.com
You can also find a 3rd grade staar math benchmark in my store. The new 3rd grade test is actually updated for 2015. Enjoy!