The Prime Minister's Committee on Natural Science in Education in Great Britain reported in 1918 that "...in many schools more time is spent in laboratory work than the results obtained can justify." Seventy years later this conclusion can often still be drawn. This is particularly a problem in open distance education where laboratory practicals, due to philosophical and logistical reasons, must be kept to a minimum and where their implementation must be both effective and efficient. Many feel that laboratory experiments do not usually justify their costs because they are all too often used to achieve the wrong goals. They often focus on the illustration or affirmation of the substantive structure of science, whereas their strength lies in the teaching of the syntactical structure of that same domain. Three common but faulty motives for laboratory experiments were rejected and three new, more valid ones were presented in their place. Finally, three types of laboratory experiments were introduced and paired, on didactic grounds, to the three valid motives. (Author/MVL)