The Edinburgh company, formerly Crocodile Clips, produces online games to promote learning aimed at children of primary school age.
Dominic Sharratt, Sumdog's marketing director, claims that the company's success reflects growing realisation of the power of "children learning without realising they are learning".
Sharratt added: "We want to make sure we are the best at what we do, we don't want to diversify too much before we've got the product right."
Sumdog's most successful program, from which the company takes its name, has six million users throughout Britain and the US, with three-quarters of them based in the States. Sumdog the program consists of games in maths, reading and writing, with the ability to choose the topic and skill level, thus ensuring accessibility for children at all stages.
Users are initially attracted to the free maths games and competitions on the website. Buying a yearly subscription - £1 per student per subject - broadens the range of games and topics available.
Teachers also play an important role in the ongoing development and promotion of the software. Sharratt said: "If in the morning a teacher suggests a tweak or change, we will have it changed by the afternoon."
But Sharratt remains adamant that Sumdog games are not a replacement for a textbook. He said: "Teachers teach, but we provide the tools for teaching … Parents want children to learn and children want to have fun; Sumdog combines education and fun in a way without compromise to either."
Since its establishment in 1995 the company has grown steadily, now employing around 20 staff.
Sharratt said: "The future is to be the best and most successful online education service in the core areas of maths, reading and writing, and take it to other countries."
Last month Sumdog was crowned winner of the Scottish E-Commerce Exporter of the Year Award.