This assessment can be used at the beginning of your addition unit. It's a useful to see what your students can do. It covers everything from adding 1 digit plus 1 digit all the way up to 3 digit plus 3 digit with regrouping.
2.OA.2: Fluently add and subtract within 20 using mental strategies.
2.NBT.5: Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or relationship between addition and subtraction.