This dissertation is devoted to the study of three different topics under the advice of three different mayor professors. The only thing these topics have in common is the interest and curiosity of the author to explain real life events, using applied econometric techniques. Chapter 2 applies financial tools to assess whether stock values reacted across world markets to the announcement of indexes that synthesize the environmental performance of the world's largest publicly-traded companies. The environmental index selected for this purpose is the "Global 100 Ranking" (G100), a ranking of the 100 largest public companies by market capitalization. The results show that the market reacted to the "Global 100 Ranking" by changing the relative price of the stocks, but not the value of the portfolio. We also find that investors in US-traded stocks are more interested in past environmental performance than on managerial quality, while the opposite is true for investors in non-US-traded stocks. Chapter 3 estimates simultaneous equation models of barge and railroad rates for specific origin-destinations and grains (corn, wheat, and soybeans) in the US, using data from the Grain Transportation Report. Evidence of specific route competitiveness of various grains was found. Interestingly, it was possible to identify a railroad route with prices as complementary of barge rates, which may increase railroad market power. River levels affect barge rates, but there are differences for corn and wheat, possibly due to production locations in the Mississippi basin. Ocean vessel rates affect barge rates directly and railroad rates indirectly. Real exchange rates affect barge rates more than railroad rates. Evidence suggests that distance between railroad origin and barge origin affects the impact of the later on the first one. Chapter 4 studies the effect on early education achievement of keeping the same classmates as in the previous year by utilizing the unique nature of the Tennessee Student Teacher Achievement Ratio (STAR). Results show that keeping all kindergarten classmates vs. losing all of them increases the probability of passing first grade by 7 to 10 percent. In addition, noncognitive skills are improved when more kindergarten classmates are kept as first grade classmates. If all classmates are kept together vs. staying alone in a new class, motivation and selfconfidence may increase by 0.5 of a standard deviation, while the number of absences may decrease by 2 to 3 days.