This bulletin describes two phases of an experiment in examining science, one in 1963, and the second in 1964. The first phase of the experiment explored two forms of assessment: a Scientific Thinking paper; and a Practical paper. In the second phase two further factors were introduced: a Facts and Principles paper; and an Assessment of course work. These papers are discussed in great detail under the major headings of: Organisation; Structure of the Trials; Relative Weighting of Examination Aspects; Marking; External Moderation of Internal Papers; Statistical Treatment and the Use of Teachers' Forecasts as a Criterion; The Scientific Thinking Paper; The Practical Paper; The Facts and Principles Paper; The Assessment of Course and Oral Work; The Examination as a Whole; Follow-Up Meetings; and Summary and Conclusions. The appendices include the test papers, instructions on assessing course work, and a list of schools taking part in the experiment. (LS)