Pressure vs Volume
Students did a lab in which they varied the volume of a closed container (syringe) that was connected to a pressure sensor while maintaining a fixed number of gas particles in the syringe.  Students graphed the data and discovered an inverse relationship between pressure and volume. In other words, when volume is varied, the pressure of the gas varies inversely.  Pressure is proportional to the inverse of volume.
 
Pressure vs Amount of Gas Particles (n)
Students did a lab in which they varied the amount of gas particles (students called them 'puffs') within a fixed volume.  Students injected 2 puffs into a fixed volume container and then measured the pressure.  Students repeated the process aforementioned until they had enough data to graph their results.  Students discovered that pressure is proportional to the number of particles added to the fixed volume.
 
Pressure vs Temperature
Students did a lab in which they collected air pressure readings of fixed volumes of gases that were sealed in a flask at 20 C and 97 kPa. Temperature of each flask was varied from -3C to 90C.  Students graphed the data and discovered it to be linear, but not proportional.  Students then projected an x-intercept of approximately -273C which would be the theoretical temperature when gas pressure is 0.  Students were shown that by recalibrating the temperature scale so that when there is no partical motion, the temperature could be zero.  Students were then introduced to the Kelvin scale (absolute scale) and discovered how to convert C to K.  They also discovered that pressure is proportional to temperature (Kelvin).

 

Other Gas Relationships

Volume is proprotional to # of gas particles (n).