When having students complete this curricular unit, you may choose a variety of methods. It is recommended that students work in small groups (3 people) so they can collaborate. You may choose to group students of similar ability level or by mixing ability levels. None of the three components makes it significantly more difficult to create a best-fit model, but adjustments to the arm-length are the least complicated to explain when it comes to discussing the affects of the alteration on the equation. If you choose to group by similar ability, give the arm length testing to your lowest level group.
Additionally, you may choose to have groups perform trials for each component of the catapult (arm length, angle of release, spring torsion) or assign specific groups to test individual components. There are, of course, benefits to both strategies.
With the first, every group will collect data, which will provide the class with a much larger set of data. By the law of large numbers, this means the data will more accurately reflect the true value. Note that to use this strategy, all groups must have identical catapults. This will work particularly well if you have chosen to use the suggested catapult kit. On the other hand, it is impossible for each catapult to be exactly identical, so each catapult will result in slightly different results. Experiments are meant to be replicated, though. Using multiple (let's say nearly identical) catapults will allow students to discuss the role error plays in experimentation.
The biggest benefits to the second strategy are time management and meeting the third CCSSM practice standard. By assigning groups to test one specific component, you reduce the amount of time required for experimentation by two-thirds. This also gives students the opportunity to share their data with other groups and to serve as an authority on the subject. This will increase intergroup dependence and require individuals to rely on other students to meet their collective goal. It also facilitates the process of constructing viable arguments and critiquing the reasoning of others (CCSSM Practice Standard 3).