This large-scale study describes what children know and can do when they start school in Scotland. The description became possible because a third of Scottish Authorities are involved in a single, broadly based, on-entry baseline assessment of children. The study also looked at variations by home background, sex, age and pre-school experience within Scotland. Comparisons were then made with the cognitive development of children starting school in England, New Zealand and Western Australia, concentrating on children whose first language was English. Surprising differences were found between Scotland and other countries. New Zealand also stood out on some measures. The results are discussed in terms of pre-school provision and what on-entry assessment can and cannot tell us. (Contains 8 tables, 6 figures, and 5 notes.)