First grade is a time when kids really have a chance to identify themselves as readers. Often times they will still need a parent close by to help with tricky words, but they will be able to read more interesting stories. Even though I included it on the kindergarten list, Elephant and Piggie is one of my favorite book series for this age too. They are so fun and they vary in difficulty. Some of them really are more first grade than kindergarten reading level. Below are some other suggestions based on what our family has found to be the best book series for first grade.

[Update: As I mentioned in my updated Kindergarten series post, there is a lot of value in teaching kids to read using decodable books. If your child is still working on understanding phonics concepts (basically the sounds letters make on their own and in pairs or groups), then I recommend starting with a decodable book series. I am presenting some of the same ones here again that are on the kindergarten list.
Note that these first grade books are targeted at 6 and 7 year olds. However, remember that all children are different. Whatever your child’s age, they will have the most success if you find books that are at or just above their current reading level.
First Grade Book Series
Beanstalk Books Decodable Readers

In kindergarten, I recommended getting a box set if you can afford it, as these series are great ways to help a child who is starting to learn to read and progress through all the levels. If your child is already in 1st grade and knows most of their letter sounds, but just needs some extra practice to build skills, it would make sense to skip the box sets and just go for the bundles that are at or just above their current reading level. According to Beanstalk, these are books that are at about Phase 5 or 6. Here is a page of books in their shop that they have deemed at a first grade level. While these are quality books, they are expensive. If this is out of your budget, check out the free online decodables from Just Right Readers.
Whole Phonics Decodables

This is another set of decodable books that I recommended for kindergarten. If your child is in first grade and close to reading at grade level, I think the Level 2 pack is probably the most appropriate. This is what I did with my own child, though really I was just trying to save money and he probably should have started with Level 1. These books are pretty fun, though the grammar is sometimes a little unnatural sounding. I think these books had a big impact on my dyslexic child learning to read comfortably. Decodables can get expensive. If this is out of your price range, I recommend the free online decodables from Just Right Readers.
Pigeon Books

Once your child has worked their way through the Elephant and Piggie series, the pigeon books are the next logical step. Mo Willems is a genius. These books are just as hilarious, but slightly more complicated for the more sophisticated reader. My kids enjoyed having these books read to them when they were in preschool and my fourth grader still picks them up and reads them once in awhile when he finds them out.
Fly Guy

My oldest child loved the Fly Guy series. They were probably the first books he started reading entirely on his own. Every time we would go the library, he would try to find another Fly Guy. I honestly didn’t read very many of these, but he thought they were funny. Even when he had progressed passed this level, he would keep checking these out from the library and I wouldn’t say a thing.
Little Critter

I remember reading these Little Critter books with my grandma when I was a kid. They are cute and sweet and make good books for a child and parent to read together. There is a spider and mouse on each page for the child to find. There is no particular order to this series and some of the books are probably more second grade level than first grade. Check arbookfind.com to find the BL (book level) of a particular title.
Biscuit

We got a set of these books about Biscuit the dog from Costco and my daughter really liked them. We read some of these together, but this is probably the first series that she started reading on her own. For cat lovers, there is another similar set about a kitten named Mittens. Both sets are part of the My First I Can Read series.
Related Links:
Best Book Series for Kids
Best Books for Kids
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