I agree with what someone else said- that maybe they should either go by school grade or incorporate that WITH the age groupings also. It would help with children who are one age but because of different reasons might be in a lower grade and feel more comfortable with younger children rather than their actual age.
It would really help keeping them with their "peers" if they were in a group of children in the same grade as them IMO. For instance, like someone else said... if either of my older two children were to bring a friend with them- they would most likely be different ages and POSSIBLY in an entirely different age group depending on the ages of both at that time, yet be in the same class at school in the same grade- yanno? What a bummer if you brought a friend and couldn't spend the time in the labs with them the entire cruise.

(my older two had to wait until almost 6 to start kindergarten due to their birthdays being after the first day of school- therefore the majority of their classes are younger than them- some by almost a year younger) So for instance- next year during our cruise when my oldest will have just turned 11- I thought they had 8-9yr olds then 10-12yr olds? But I just saw a post that said 8-10yr olds... so I assume that means 11-12yr olds together then 13+ together, right?
If so, when we go on our cruise- my daughter will have just turned 11 yrs old like 10 days before the cruise- and she'll be with 11-12yr olds while most everyone in her classes at school are 10yr olds... she's not going to be used to being around 11 & 12yr olds. Most everyone in her class will not be turning 11 until after her or the following summer. Might not cause a problem with HER- but might for other children? And since schools are very strict nowadays with the age minimum before starting school- it can really make the ages older yet in lower grade... so then they go on a cruise with children older than they are used to in their classes- for instance.
For instance when she's 13- she will be 7th grade where other 13yr olds might be in 8th grade... she'll be in a class with other 12yr olds and in middle school where all are 11-12yr olds except the ones that turn 13 during the school year like herself. On the cruise she'd be with 13yr olds and up..
and up!!! Which is why I probably won't schedule another cruise until she's much older and more mature (after the one planned now for 2005) because there's no way at barely turned 13 and in 7th grade with 12yr olds (in a school that is all 10-12yr olds with only some turning 13 towards the end of that school year) that I'd want her in a grouping of 13-17yr olds on the cruise. Uhuh... nope. I wouldn't be able to enjoy myself the entire time- I'd be worrying about her being with all those older teens. LOL