The question asked is simply, "Find the angle that a projectile needs to cover the largest horizontal distance." That's it. The kids can use several types of projectile launchers. Real ones like the PASCO Marble Launcher or Sargent Welch's Projectile Launcher. Toy ones like Mini-Frisbee Launcher, Super-Soaker (YES, water IS a projectile when done properly), sling shot toys.
After they have, thru repeated data, found the angle to be around 45o, I then will teach the range equations to verify what they just found out.
I am convinced that the kids learn more thoroughly when they do the discovering.