In this lab, students are tasked with calculating where a marble will land when it rolls off a level table top. They will then use their calculations to place a target at the point of impact and have their teacher watch the result. I make sure my students understand that if their marble hits the ground before the actual test run, they will get a zero on the lab. The point of the lab is not to see where a marble will land, but to calculate where it will land. Therefore, students should not know ahead of time where the target should be placed.
This lab is a direct application of horizontally-launched projectile problems (like a car driving off a cliff, for example). Therefore, students should have a solid understanding of such problems.
I have found, with my advanced classes, I can leave the students on their own with this lab and usually just give them the premise, leaving them to complete it on their own. However, with my regular physics classes, I usually have to offer a little more guidance. This is also a lab which works wonderfully in 90-minute class periods, but is much more complicated to complete in 45-minutes if there are several different groups needing to test their calculations. Therefore, it is suggested, in 45-minute class periods, that prep work is done the day before the lab to allow students a better understanding of what they will be doing. :)
*NOTE: This lab is intended to be used with iPads or iPhones where students have access to video apps that allow frame-by-frame playback with timestamps. The app we use in my classroom is Coach My Video.