What about Reading Levels?
Reading levels matter only for a couple reasons.
Younger readers
When you have young readers (the elementary school set) you want to make sure that the books they are reading are around the right level. Books that are too difficult can frustrate a reader or take a super long time to read. It also can help parents figure out if other books will be achievable for their kids based on the lexile of recent books they have found. Lexile measures are not always available (and are rarely available for books that target the older young adult audience).
If they're reading for school.
Many schools require their students to read books that are within certain lexile or reading levels when they are reading for school.
Reluctant Readers
When trying to entice reluctant readers it is often a good idea to give them a book that is interesting yet is written at a low reading level.
A Note About Reading Levels
Lexile levels only access the difficulty of the text -- and they do so by calculating things like sentence and word length (like Word used to after you spell checked your essays in college). They do not access the difficulty of the plot or the age appropriateness of the text.
Most fiction (even on the adult market) is written no harder than a middle school reading level, unless your child is required to read at a certain level for school (or is reading specifically to increase their reading level) do not discourage them from reading a book because it is "too easy". If they are reading more difficult books for their required reading for school they can read easier books on their own time before they go to bed.
Books that are written at super high lexiles include books like the ones you read in your high school and college literature classes and non fiction like your child's science textbooks. Here's a list of some very high lexile books if you are interested Books with a lexile of 1000-1500.
Here is a chart that has a basic lexile conversion to grade levels.
Length Matters: When determining if a book is appropriate for your younger reader it is important to not only take the reading level but to check out the length of the book. If a book is harder than what your child usually reads but is short it could be a good book for them to work on their reading skills. Likewise books that are easier than your child generally reads but are lengthy can help them to work on reading quickly (and feeling success in finishing that big thick book). If a book is harder than your child normally reads and very long the chances are larger that it will prove frustrating to your reader.
Audio Books
Audio books are a terrific way for kids to listen to books that are too difficult or too long for them to read alone (and to pull out if they are enjoying a story but are frustrated by the reading level or length) and also for them to receive the benefits of being read to when they have decided that they are too old for a bedtime story (my daughter decided this right after Kindergarten) or for them to have a book read faster than one night at a time. Audio books can be used alone or with a hard copy of the original book.
If you have small children you can record yourself while you are reading to them (there's a great record feature on your ipod) and then they can listen to the stories read by you over and over again.
Remember the #1 Rule
If your child wants to read something then let them read it. It's not bad to mention that a book could be very hard, but the ultimate decision should be up to your child. Unless a book is severely inappropriate then the decision to read or not read a book for pleasure should be up to the child.
, 
, 
and the fourth book 
which will be released in late May. These books follow ten year old cousins Jessie and Daisy who find that that the geode that they picked up while on a hike hatches revealing a talking baby dragon which they name Emmy. Jessie and Daisy have to take care of Emmy and protect her from the evil St George who uses dragon blood to stay alive.
will be released in early May.
`
. The revolution is over and work has begun expanding the inside to higher levels so the population of the Inside can spread out. Unfortunately, things have not turned out as well as hoped since the revolution. Scrubs are bitter about having to work while they feel the uppers are living in luxury, the newly formed committee is not getting anything done and someone has been sabotaging important systems putting the Inside at risk for destruction.
by Mari Mancusi is the second book in the Blood Coven Vamire series. It follows Rayne (sister of Sunny and lover of vampires) as she finds out that she is a Vampire Slayer. While she initially balks at the idea she agrees to help find out what has been going on with a vampire who is trying to take out Magnus (Sunny's boyfriend).
and the rest of the Jessica Darling series. Judging by her past work this should be an excellent book for the high school aged audience.
will be released on May 1st. 
than other horrifying dystopian societies that have been popular in recent dystopias such as the Hunger Games. Her society is seemingly perfect but also heavily regimented and controlling. To make things more frustrating everytime Cassia does something that she feels is out of the ordinary one of the officials tells her that she was predicted to act in that way. She's never overtly threatened and there is no risk of bodily harm but there is always a risk of being watched. The romance and love triangle which is heavily featured in the story is sweet. There is a large focus on poetry and art which could encourage younger readers to seek out the poem that Cassia treasures.
and 
is not just a modern retelling of one fairytale. It takes elements from several less known fairy tales and combines them. The result is a fun and original tale with just the right bit of romance and action. It is a light and fluffy story and a very quick and easy read (I finished it in about three hours). 
for a long time. It's a modern retelling of my favorite myth Persephone. From Meg's Website: