The Four Pillars of Educational Games (4PEG)

is a model for evaluating video games for use in formal learning situations, especially the classroom. It includes The Magic Bullet, which is a simple visualization of the learning in a game.

This website also contains resources and additional support for the book:

Choosing and Using Digital Games in the Classroom – A Practical Guide

by Katrin Becker

Published in 2016, as part of the Springer Series in
Advances in Game-Based Learning
Series Editors: Dirk Ifenthaler, Scott Joseph Warren, & Deniz Eseryel
ISBN 978-3-319-12222-9

For those at educational institutions, Springer offers offprints at a highly reasonable price, called MyCopy. Check it out!