First of all,
At the acceleration meeting, after the school had already made their recommendation, they mentioned that DS's score on the IAS was a 1.5?
I think they were playing you. The IAS reports scores as a number from 0-80:
34 or fewer points: Acceleration is not recommended: Consider single-subject acceleration, mentoring, enrichment, or other alternatives.
35-45 points: Marginal candidate for whole-grade acceleration: There is no clear recommendation. Review materials closely and carefully consider curricular alternatives.
46-59 points: Good candidate for whole-grade acceleration: Acceleration is recommended.
60-80: Excellent candidate for whole-grade acceleration: Acceleration is recommended.
1.5 as a total doesn't make any sense whatsoever in regard to the IAS.

There was suppose to be parental input? You mean the school was supposed to do something other than fill out the IAS themselves??? We were never made a part of the process of filling out the IAS.
Oh yes. From the manual itself:
"Team members may include one or two educators, an administrator, a counselor or school psychologist, the student's parents, and the gifted teacher if there is one.
...
To save time, the school psychologist might be asked to gather and report on all the test scores needed for the first two or three pages of the Form, while the classroom teacher(s) might be asked to gather current grade reports, standardized test results, and portfolio work.
The team meeting or staffing will take anywhere between 1.5 to 2 hours. It should begin with a discussion of the purpose of the IAS. In the meeing, half of the time will involve discussion and filling out of the IAS form, while the other 45-60 minutes will be used to create an implementation plan by using the IAS Summary and Planning Record.
The thing is, the IAS Manual offers some important hints in the "fine print" that the school may not pick up on but a parent certainly will -- in the instruction section. For example, it says that if you don't have an aptitude test, you can give an above level standardized test -- or norm the MAP, for example, against older kids, which is really easy to do. There's a ton of information in the back section of the manual too -- the sort of information that won't be read unless you're actually interested in using the thing right. Unfortunately, doing it right takes extra time, planning and thought.
Here's the Participation in School Sponsored Extracurriculars section. That section is worth 0-3 points, with options:
--School activities are available for the studen's age or grade level, but student does not participate: 0
--Student shows limited paricipation in available activities: 1
--Student participates in two or more activities and does well, but has not received special recognition: 2
--Student has a leadership role or has received recognition in one or more activities: 3
On the face, my kindergartner hadn't done *any* of these options -- nothing was available for him as a Ker. But in the instructions section, it states that the team needs to consider outside (non-school sponsored activities) if there's nothing at school. So my ds's score would have gone from a 0 to a 2 right there. And when 24 points are made up of testing alone, those 2 points on 5 or 6 different questions make huge difference in the end recommendation.
Or look at the "motivation" question. The options are:
--Student does not complete assignments and appears disinterested in schoolwork: 0
--Student completes those tasks that are of interest to him: 1
--Student completes virtually all assignments on time and shows a positive attitude: 2
--Student completes most assignments more quickly and comprehensively than other classmates: 3
Well, my ds was between 0 and 1 from the school's point of view ... he'd not color in the "b is for bird, now color the bird blue" worksheets and would instead doodle on the back of his papers. Was it because he was not into learning? No! He wasn't interested in coloring to reinforce colors and letters. It was dull, so he wouldn't do it. Is that fair, when he was doing advanced worksheets at home? I'd have given him a 2, because at least, when appropriately challenged, he'd enjoy the work.
It was a moot point for us anyway, as he was 1 point short of the "good" category -- without any out-of-level testing -- and they wouldn't discuss it. In fact, they flat out said that they wouldn't consider accelerating anyway unless he was near the top of the "excellent" category. So it was basically an exercise in making us sit down and shut up.
Well, we shut up and left the school.

ETA: Ah, maybe in the older edition the scoring was different? That would explain the 1.5, at least ...