I think many people have a skewed view of GT students. GT does not equal high academic achievement. As a matter of fact there is a lot of literature out there on the lack of motivation (I won't say laziness) in GT students. The fact is, they are clever enough to figure out quickly how to do the minimum in order to get by. I have also had several students through the years with learning disabilities or who were ESL-their classwork does not show what they have the potential to do. Our district has now made a goal for all GT students to achieve commended status on their standardized testing. I think it's a really unfair standard. Yes, they possess an innate ability to pick things up quickly, but in this age of teaching to the test and ignoring the kids who can already pass, teachers don't often spend as much time with the advanced kids. They often don't show a much growth. And it is hard if a 3rd Grade student is already reading at a 5th Grade level to give them the skills they need to move up to a 6th or 7th Grade level-but it can be done. Instead our focus is on the struggling students and our poor GT kids just kind of stagnate.
Anyway, just to prove a point. I have a very bright class-they are creative, well-behaved (for the most part :) and most of them are eager to learn. For the 100th day I challenged them with working in pairs to be the first group to come up with exactly 100 counters-I wanted to see if they could apply what we've learned about grouping. They all used different manipulatives and we had a little competition. Now bear in mind, we have spent a good amount of math instruction this year on place value. They've been counting by 10's, 5's and 2's since Kinder. Only one group figured out it was faster to group them and count rather than counting by 1's and losing your count again and again. Of course, I explained it to them and if we played again, I bet many more students would apply that and count by 10's-but it's not automatic. They still have to be taught!
Even in Kinder-they begin the year, most them not being able to read. Even if they can read, you still have to teach them phonics rules and end up teaching them backwards, because they can already read the word but have no idea why. I had a parent once brag that their Kinder child could multiply-sure he could rattle off the facts, but had no idea what that process meant or when to use it, how to apply it. You should see how much patience it takes to teach them how to compare and contrast. "How are these 2 things different?", "they're just different.", "ok, but in what ways?", "they are different things." Ugh. Once they get it they can apply it readily, but getting there is like pulling teeth.
Anyway, my point is GT/advanced kids still need to be taught. They still need to meet with you in reading groups. If they finish the work in 2 seconds, they should have a more challenging activity-- not sit there reading a book or even worse yet, my pet peeve-"Johnny, why don't you go around and help the students who aren't finished yet". It's really ok to give different students different work! My class has 2 different sets of spelling words. I give out 3 different comprehension passages for their tests. If you're testing comprehension it should be at their reading level-if they can't read it, they definitely can't comprehend it.
All kids deserve to grow academically!