What are the differences in teaching quality in countries with large cultural and economic differences, such as Nicaragua, South Korea, and the Netherlands? Can these differences be bridged with training programmes? In Nicaragua, South Korea, and the Netherlands, respectively 271, 407, and 144 English and mathematics teachers in secondary education were observed by specially trained observers. The difference in teaching quality between Nicaraguan teachers and teachers in South Korea and the Netherlands is about 1.5 "SD". The difference between Dutch and South Korean teachers is about .13 "SD". After 160 hr of teacher training, in combination with training of observers in reliable observation, the Nicaraguan teachers grew slightly more than 1 "SD". Further research should check whether a growth in teaching skills of teachers in developmental countries is accompanied by a growth in learning performance of students.