This paper measures empirically the relationship between classroom teaching practices and student achievements. Based on primary- and middle-school data from Israel, I find very strong evidence that two important elements of teaching practices cause student achievements to improve. In particular, classroom teaching that emphasizes the instilment of knowledge and comprehension, often termed "traditional"-style teaching, has a very strong and positive effect on test scores, particularly among girls and pupils of low socioeconomic background. Second, the use of classroom techniques that endow pupils with analytical and critical skills ("modern" teaching) has a very large positive payoff, evidenced in improvement of test scores across subgroups differentiated by gender and socioeconomic background. However, the effect of each of these two teaching-practices are different at different treatment intensity, the first has its highest effect at low to medium levels of treatment, while the second has its largest impact at high levels of treatment. I also find that transparency, fairness, and proper feedback in teachers' conduct with their students improve academic performance, especially among boys. However, I find no evidence of an effect of a second element of modern teaching, instilment of the capacity for individual study. Apart from identifying "what works" in the classroom, these findings yield two insights for the debate about the merit of "traditional" versus "modern" approaches to teaching, which are often discussed as rival classroom pedagogical approaches. First, one approach does not necessarily crowd out the other; both may coexist in the classroom production function of knowledge. Second, it is best to target the two teaching practices differentially to students of different genders and abilities. The effect of the effective teaching practices estimated is very large, especially in comparison with that of other potential interventions such as reducing class size or increasing school hours of instruction.