  Mechanical TA 2 (MTA2) is an open source web-based peer grading application
that leverages trusted TA graders to incentivize high-quality peer review. A
previous, prototype implementation of MTA proved the value of the concept, but
was neither suitable for use at scale nor easily extensible; MTA2 is a complete
reimplementation of the system that overcomes these hurdles. MTA2 serves two,
interconnected purposes: facilitating practical peer grading and serving as a
testbed for experimentation with different peer grading mechanisms. The system
is characterized by a modular design that makes customization easy; support for
dividing students into different pools based on their peer-grading prowess;
mechanisms for automated calibration and spot checking; and the ability for
students to appeal grades and to give feedback about individual reviews.
