Here are some links for websites that offer multiple choice practice tests for the standards taught in 2nd and 3rd grade. It's a good idea to do these with your child so you can offer support on questions they don't understand.
The California Department of Education has a website with an overview of all the Common Core Content Standards (CCCS) for third grade. The document is 88 pages long. My recommendation is that you look over the specific content areas of language arts and math to get a clearer view. There is a shift currently from the old state standards to the Common Core.
Your child will be tested using the California STAR test again this year, but starting next year, they'll be tested on a computer in a new format that is called adaptive testing. I'll be working towards integrating the CCCS into my curriculum this year.
I highly recommend viewing or downloading the CCCS so you can see what is expected of your child this year. You can also go to the Smarter Balanced website to see sample questions from this new form of assessment. Scroll down after you click on this link and you'll see some links for English Language Arts and Math.
Language Arts Assessments
Reading Comprehension Assessment - This is very similar to the STAR test format that students will take in April. It requires you to go back into the text to find your answers. Please do this with your child.
Comprehension and Sequence - This test practice focuses specifically on paying attention to sequence words like first, second, third, next, and then. The passages are shorter than the first test.
Proof reading - Here you're given sentences that are written incorrectly and you need to correct them. The primary focus is on writing conventions like capitalization and punctuation.
Prefixes, suffixes, and context clues - On this practice page, your job is to create a word using either the prefix or suffix that's supplied. Once you've created the word you're given a sentence and you need to decide if the word works contextually within the sentence. If not, you request a new word. Adobe shockwave is required to make this game work.