The defining features of contemporary prevention science are high-quality empirical research that uses rigorous and proven scientific methods, careful hypothesis testing, and the systematic accumulation of knowledge in a manner consistent with other areas of science. Understanding the etiology and prevention of juvenile substance use has increased substantially over the past two decades. Prevention approaches typically target the use of tobacco, alcohol, and marijuana, because these are the most widely used substances in American society and because experimentation with these substances occurs in the early stages of drug use and abuse. One example of such a prevention program is the LST program, a universal, school-based prevention approach to juvenile drug abuse prevention that has been extensively tested over the past 25 years. Over time, the intervention has evolved from preventing tobacco use to the prevention of other forms of substance use with different types of program providers, under different intervention conditions, and with different populations. This paper traces the use and development of various evaluation methods applied to LST, including small-scale efficacy trials, large-scale effectiveness trials, and independent research. Taken together, the results from three large-scale randomized effectiveness trials have produced strong evidence of the effectiveness of the LST approach with a variety of target groups in various settings. This conclusion is contrasted with Dennis Gorman's conclusion that LST evaluation studies have not been sufficiently scientific (See NCJ-210365). 1 table and 43 references