The Calculus for Kids project was deliberately designed to use computers in the transformation of curriculum. The intervention used multi-media learning materials to assist teachers and Year 6 (aged 11-12 years) students understand the principles of integral calculus. They used Maple mathematics software to solve real-world problems using these principles and by employing conventional mathematics notation on their individual computers. Between June 2010 and April 2016, it was implemented in 23 classes at 19 schools involving 434 students. Two methods were used to calculate effect sizes of 22.19 (pre-test/post-test Cohen's d) and 1.17 (age-maturation). Positive gains were also found in students' attitudes, particularly in Technology confidence. This article discusses methods for calculating effect sizes for transformational education with computers and recommends further research in the field.