The article deals with the problems of a school experiment meant as a cognitive process. The experiment is considered not only to be a means but also a subject of a lesson. The structure of the school experiment is worked out in four basic stages (goal, preparation, implementation, evaluation), which are logically divided into single steps. The above mentioned structure was tested in lessons of chemistry according to the text-books for the experimental work of basic and secondary schools pupils. The practical results verified the assumption that the proposed process acquaints the pupils with the experimental method which is the resource of empiric knowledge, and makes the systematic preparation, control and evaluation of educational process possible; and contributes to activity and independence of pupils and helps to understand and remember the subject matter.