For the both middle school and high school levels, the same process can be followed.

Moderator/Instructor organizes groups of 3 or 4 in your class.

Each group tries to project the cannonball in this tool.

They have a table to note all the variable that they try. (Angle, length of the line segment, gravitational acceleration...)

They endeavor to make some inferences about the relations of these variables.

Depending on their inferences, they make several estimation on the possible length of the red wall for some given angles.

It's an inevitable fact that instructor will be going around his/her students to observe and direct their discussions, and to mould his/her lecture in a more productive way.
Note: In high school level, several calculations or expectations of some exact solutions can be added to this steps.