They said once in a Q&A that they start controlled crying at 6 weeks. When they are old enough to climb out of their cot take the door handles off to stop them coming out of the room. They consider that to be sleeping through the night.How do the Radfords always manage to get babies who sleep so easily my 8 month old twins still don't sleep through the bloody night how can such a tiny baby be sleeping until 9am!