I have the greatest respect for Jeff Anderson and if students read all of his forum comments carefully, they will have an excellent framework for success with this event and for a fulfilling science experience. I do however have a slightly different perspective on use of kits like the one available from Freedom Flight. I am an experienced indoor flyer and an occasional competitor and have coached several high school science olympiad teams in elastic launch glider and Wright Stuff and other indoor rubber powered airplane events for the last eight years. As the time required to construct a high-quality Wright Stuff airplane is a pretty fair commitment for the students, and as I have found that a number of students involved in SO are also involved in other activities, limiting SO time to a certain extent, I like the idea of using the Freedom Flight kit in order to get construction done as efficiently as possible and allow more of the student's time for testing, data recording, modifications and learning a systems approach to problem solving.
The four high schools that I coached last year constructed eleven Freedom Flight kits in total. All flew over 3:15 in gyms with the usual 25 ft. 27 ft. ceilings. The team that put the most effort and time into the project, Holt High School, won the Michigan State SO Championship with a flight of 3:46 in a 21.5 ft scrubbable ceiling gym. They also won two of the larger invitationals in mid-Michigan with similar results. The modifications the students made to these kits are described (and pictured) in the 2015 SO Wright Stuff forum. These kits fly great!
I agree with Jeff that for the same money as a Freedom Flight kit package (which constructs two airplanes) you can build about five airplanes from scratch. However, unless you already own a stock of reasonable quality balsa wood, or have a local source to purchase balsa wood, it can be a little tricky to get the wood you need without buying a few sheets of each size by mail order. The rules for this year do not require especially good quality wood, but, in my opinion, it would be a good idea for the fuselage and tailboom to be a maximum of 8 lb/cu ft density range and the wing and stab spars to possibly be a little more sturdy (maybe 12 lb, or very stiff lighter wood). Buying a few sheets of each size will ensure that some of the wood will be in the correct density range. Remember too that even if a sheet of wood is in the 10 lb range, it might actually be made up of sections of 8 lb and 12 lb wood and you can cut from the various sections of the sheet to get the result that you want. These weight ranges (with reasonable grain and stiffness) should easily bring the airplane in underweight and most likely make it sturdy enough to handle the high speeds required by the ballast bonus.
Good luck and good science.
AMA since 1972 (off and on)
NFFS also for a long time (off and on)