The use of apparent time differences to study language change in progress has been a basic analytical construct in quantitative sociolinguistics for over 30 years. The basic assumption underlying the construct is that, unless there is evidence to the contrary, differences among generations of similar adults mirror actual diachronic developments in a language: the speech of each generation is assumed to reflect the language more or less as it existed at the time when that generation learned the language. In providing a mirror of real time change, apparent time forms the basis of a conceptual framework for exploring language change in progress. However, the basic assumptions that underlie apparent time have never been fully tested. This article tests those assumptions by comparing apparent time data from two recent random sample telephone surveys of Texas speech with real time data from the Linguistic Atlas of the Gulf States, which was conducted some 15 years before the telephone surveys. The real time differences between the linguistic atlas data and the data from the telephone surveys provide strong support for the apparent time construct. Whenever apparent time data in the telephone surveys clearly suggest change in progress, the atlas data show substantially fewer innovative forms. Whenever the apparent time data suggest stable variation, the atlas data are virtually identical to that from the more recent surveys. Whenever the relationships between real and apparent time data are unclear, sorting out mitigating factors, such as nativity and subregional residence, clarifies and confirms the relationships. The results of our test of the apparent time construct suggest that it is unquestionably a valid and useful analytical tool.