In 2009, the government's Department for Education commissioned a team of researchers at NatCen Social Research to evaluate the effectiveness of the youth development/teenage pregnancy prevention programme 'Teens and Toddlers'. Previous studies had positive findings but had not been very rigorous in terms of methodology and methods used. We evaluated the programme through a randomised controlled trial, in collaboration with the London School of Hygiene & Tropical Medicine and Bryson Purdon Social Research. This case study provides an account of the stages in conducting a randomised controlled trial, from the initial scoping out of what exactly we were going to measure, coming up with the randomised controlled trial design, to reflecting on the possible methodological limitations of our research. It gives a narrative of the whole 'RCT journey' -- how we determined the outcomes to be measured, the factors that enabled and limited us in designing the randomised controlled trial and the methodological and practical challenges the research team encountered along the way and how we dealt with those. [This content is provided in the format of an e-book.]