This report presents some of the results of two national surveys which assessed the performance of 13-year-old students in science. It includes an outline of the assessment framework; some of the questions which were written to match it; a description of how well, and how differently, students responded to the questions; and suggests how the information might be used. The 1980 survey involved 448 English schools while the 1981 survey, which included Wales and Northern Ireland, involved a total of 556 schools. Performance of the 13-year-olds as a whole (represented by mean scores) rather than performance of individual students was the focus in each survey. Areas assessed included: use of graphical and symbolic representation; use of apparatus and measuring instruments; making and interpreting observations; interpreting presented information and applying biology, chemistry, and physics concepts; planning parts of and entire investigations; and performing entire investigations. Among the reported results are those indicating that: (1) although differences exist in some areas, performance levels of boys and girls are similar; (2) there appears to be a mismatch between student performance and expectations implicit in science curriculum materials; and (3) estimating quantities and describing relationships appear to be difficult for many students. (JN)