Professor Portal Achievement
After completing co-op, complete Calibration Course online with a friend who hasn’t played before
First you must complete Co-op. So you have to beat all 5 courses with a friend offline or online. After you have done that, you must complete Calibration Course with another friend online who has not played Co-op yet. It is fine if they have played Single Player, they just can't have played Co-op. You can choose Calibration Course in the Hub by pressing start. Calibration Course is the Intro and Training Course for Co-op. If you want more information click here. If you're having trouble finding a partner for the achievement, post in the Achievement Trading Thread here.