 Several critics wrote that Portal 2 excels in teaching the player to solve puzzles; in a review for the New York Times, Seth Schiesel wrote, "Somewhere out there an innovative, dynamic high school physics teacher will use Portal 2 as the linchpin of an entire series of lessons and will immediately become the most important science teacher those lucky students have ever had." Mathematics and science teachers wrote e-mails to Valve to tell them how they had included Portal in their classroom lessons as part of a project to promote the "gamification of learning". Portal developers Joshua Weier and Yassr Malaika led a team within Valve to explore ways of using Portal 2 for education. This led to the development of Puzzle Maker, a level editor for Portal 2 players, built from the professional tools used to develop the game. Weier and Malaika did not want to design curricula themselves, but wanted to provide educators with tools for creating lesson plans. Hammer, the only tool freely available before the release of the built-in level editor in 2012, was difficult for educators to learn and understand. Valve gave Puzzle Maker an easy-to-learn interface and the ability to share puzzles and lesson plans. The tools were developed with a mathematics teacher and her students. This formed the basis of a new "Steam for Schools" initiative launched in June 2012, under which educators could acquire Portal 2 and the Puzzle Maker software free of charge for classroom use through its "Teach with Portals" program. As of November 2012, Valve estimates that over 2,500 educators are using the "Teach with Portals" software within their lesson plans.
