Request for controller nodes to display output values. I think thatguy suggested something similar here in a debug form.
Idea 1: show min and max values of output graphs when they update at the end of each stroke.
Idea 2: show live value readouts on each node as the stroke is created.
Idea 3: a series of graphical outputs to an external document for later review from each node.
Idea 4: a mode that displays a canvas that works like the brush preview window and a graphical output of the stroke for the controller you choose... this could be fun if it worked with the stroke modifier so you could see how changing a node effects both the graph and your stroke.
I still think BlackInk is just a couple steps away from being a legitimate math tutorial program.