STACK is an online assessment system for mathematics and STEM, designed to enable students to answer questions with a mathematical expression, such as a polynomial.

A STACK question giving specific feedback on a partially correct answer, including graphing the student's answer.
STACK helps students learn from their mistakes through specific feedback.

Computer Algebra Support

STACK uses the Computer Algebra System Maxima to evaluate expressions.

  • Mathematical answers: questions are not limited to multiple choice.
  • Randomise questions: so different students see different variants of a quiz.
  • Graphical support: make your questions stand out by integrating Maxima plots, JSXGraphs or Google Charts.

Validation of answers

Before answers are graded, students confirm their answer is interpreted correctly by the system. Invalid answers, like ones with mismatched brackets, are rejected.

  • Fair: students are not penalised for poor computer skills.
  • Flexible: the teacher decides what a valid answer looks like.

Intelligent marking

Teachers write grading trees that mark answers based on mathematical properties, like "is it factored?"

  • Specific feedback tailored to each student's answer.
  • Multipart questions with follow-through marking.
  • Give-example style questions with many correct answers.
  • Diverse question types involving scientific units, numerical accuracy, line-by-line reasoning and more.


As an open-source project, users help improve STACK by adding features, translations, bug reports and more. Many users share STACK materials, for example through the ABACUS material bank.
Credits and contributionsABACUS material bank

Trusted user base

STACK is trusted by many respected institutions.

More users