Commercial 4-Methylcyclohexanol (1) is a mixture of 30% cis and 70% trans isomers. A standard sophomore organic lab dehydrates this alcohol with phosphoric acid to illustrate an elimination reaction. Many lab manuals state that a pure product, 4-methylcyclohex-ene (I), is formed. C13 NMR analysis of the vinyl C atoms shows that the rearranged products 3-methylcyclohexene (II) and 1-methylcyclohexene (III) are produced also. The quantity of these increases with reaction time, a phenomenon dubbed the "Evelyn Effect". Approximately 80% of I, 15% of II and 5% of III are formed at early reaction times and 65, 20 and 15 % respectively at longer times. Dehydration of pure cis and trans isomers of 1 show similar results, with the cis isomer giving more products of rearrangement. Thus use of the very expensive pure isomeric alcohols offers no advantage over the commercial mixture for student labs. It seems likely that the isomeric alcohols may be interconverted during dehydration but this has not been established. Prolonged refluxing before distilling the products leads to more extensive rearrangement. Supported in part by a Faculty research grant from the Fordham University Research Council.