How do I know that the algorithm is picking the right questions?

Each new question is assigned a difficulty level based on highly prescriptive specifications for question types. When writing a new question we know the difficulty of all the questions of its type. These have been graded by teachers on a scale of -1 to 5. 

Atom’s algorithm takes this grading and then evaluates the responses of every child who encounters this question. Then it accurately adapts the difficulty grading if needed. As a result, we have an enormous question bank that is standardised by the Atom population (c. 150k students) from which the algorithm can choose and assign to students at the level best suited to them, based on their previous answers.