High Frequency Words
These words should be recognized by SIGHT. "Sounding out" will not always work, and your child should be able to read the word in 5 seconds. In addition, your child is held responsible for spelling them correctly when working on a writing piece.
Working on these High Frequency Words (a.k.a. "sight words") are one of the essential skills that you can help with at home. Automaticity of these words is key to improving your child's fluency, thus improving his/her comprehension.