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App review by Paul Donovan, Common Sense Education | Updated November 2014
Quadrant Defender

Quadrant Defender

Graphing equations is the key to victory in tower defense game

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Subjects & Skills
Math, Critical Thinking

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Pros: Combines algebraic thinking, strategy, and resource management in one coherent package.

Cons: Can be confusing for students not familiar with the genre

Bottom Line: An effective and more motivating way to get students to practice graphing linear equations.

Because this is a free Web-based game, teachers can recommend (or require) any student with an Internet connection to play. This can be an enrichment tool for students already familiar with solving systems, while their classmates learn the process in a more traditional way. Quadrant Defender will work particularly well with students who need more relevant, external motivation. And the different difficulty levels can be useful for encouraging competitive students to keep playing. If computers are in short supply, or students are having a hard time, it can be used with a projector as a whole-class activity in which students work together to determine correct defense placements.

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Fans of tower defense games, which force the player to protect a base by repelling invaders through clever strategy and tactics, will feel right at home; Quadrant Defender looks and feels comparable to more recent games in the genre. What makes Quadrant Defender different is that to defend his/her base, the player must solve systems of equations to find the best spots to bolster against alien invaders. This incorporates math into play in a way that feels high-stakes because an incorrect solution means the base is overrun by enemies. At its core, it might be a repackaging of practice sets, but thematic context and tower defense mechanics go a long way. 

The learning curve may be too steep to use Quadrant Defender as an introduction to solving systems, but it's an excellent practice and review resource. By default, players get to solutions by graphing, but additional tools are available for students who want to use other methods, such as addition or substitution (although these tools aren't intuitive to discover or use). In addition to algebraic skills, students must build and strengthen their defenses using a limited amount of money. Success requires an intuitive sense of constraints -- students must learn to strategize and practice resource management. Although there's only one set of "official" defense solutions, those points can be utilized in many different ways, so creative thinking skills can allow students to develop many different possibilities for success.

Overall Rating


This interesting and suspenseful approach to systems should have high replay value for students.


Designed to encourage students to practice solving systems, the game is more review than instruction. Includes an interactive "algebra explorer" for students who need it.


Students not familiar with tower-defense games or systems of equations may have trouble figuring out what's going on. Rules and hints aren't as complete as they could be.

Common Sense reviewer
Paul Donovan Classroom teacher

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