As far as the literary style and complexity of prose is concerned I would agree that it is for middle school years. However, thematically I believe that it can engage older, even college students, to negotiate complex philosophical themes which include those mentioned in other answers, but can be expanded to include the relationship between emotions and reason, moral judgment, happiness, justice, the relationship between political freedom and equality. This could be accomplished by introducing alternative readings (the literature abounds) that are more age appropriate and/or class assignments. Again this would depend upon the learning outcomes and student level.
Post 7 brings up a good point about the issues perhaps being too complex for elementary students to fully grasp. I'm not sure the idea of government-enforced euthanasia would be possible to understand for the average elementary student. I still think that gifted 5th graders could probably read the novel, though some of its depth might be lost. Some of the more complex themes of failed Utopia would be better for a higher grade level.
I think The Giver is perfect for middle school age students. The writing level and style appeal to the middle school student, as well as the content. I'm not sure that elementary students would have the sophistication to understand all the themes, while high school students might find it boring and too easy. I think it is a great book for engaging middle school students in thinking about bigger issues, because they can still relate it to their own feelings.
I agree with the other posters that this book is most appropriate for the middle to high school age group. I'm not sure that I would have wanted my daughters to read this book in elementary school as some of the issues addressed in the novel are difficult to understand and discuss for lower age groups.
I think The Giver can be utilized effectively anywhere from 5th to 9th grade... especially in a low-level 9th grade class. The content can be easily understood by a gifted 5th grader, but the themes and literary devices used within the novel can also be expanded and practiced by middle and early high school students as well. It is a great book to get students interested in reading, as most students respond relatively well to the novel.
In the school where I work, it is taught at Grades 7 and 8 roughly, depending on the teacher and what they feel happy with. It is definitely not a book for Grades 10 and above, I think, but at the same time I think you need to possess a certain amount of maturity to be able to discuss some of the issues arising from this excellent book.
Middle school is my first thought, but I have also had many low-level reading students on the high school level read this book for practice with reading comprehension and fluency. My son has read this book and he is in the sixth grade. I tend to believe that it might depend on the maturity of the child, but for a blanket audience, I vote for middle school (5-8 grades).
I agree with the previous post -- it is a great book for the middle school student. It is a rich and layered novel, but assessble for that age. It is too simple for high school students who need a more complicated plot and are ready to read and analyze for more than character and theme.
Content-wise, I think that this is a middle school book. To me, the importance of this book is that it gets students to think about how the good and the bad of emotions are inseparable, about how we cannot be open to joy if we are not open to sorrow. I think that this is a bit much for grade school kids. My daughter read the book when she was 8 and she liked it, but she really didn't get the full meaning of the theme. So I think that kids have to be a bit further along before they can truly appreciate the book.
I think that a middle school level is appropriate for the book. I personally read it on my own in 4th grade, but I was well ahead of most of the other kids in reading levels (I read Lord of the Flies as a guided reading book in 6th grade, and Anna Karenina in 8th). Any younger than 7th or 8th and you run the risk of children either not reading it, not caring, and definitely not understanding it and understanding the meaning behind it.
I read The Giver before in high school at George Little Rock. And I loved it. I think I might read it again during this summer I have to go to the libarary. And I would say 6th Grade level. Am more then a 3rd grade level reader. I get really mad at reading if I dont understand it but am praticing alot of reading right know.