Since the introduction of teaching English as a regular subject into primary schools in 1997, it has been said that the discrepancy between students who are receiving private instruction at learning institutions and private tutoring and those who are not receiving private English instruction is steadily increasing. The purpose of this study was to investigate what impact private English instruction had on English achievement and attitudes of fifth- and sixth-grade students in primary schools. For this purpose, an English achievement test was developed based on the 7th National Curriculum and administered, along with two attitude questionnaires: One questionnaire was administered to 696 fifth- and sixth-grade primary school students, and the other questionnaire given to 12 primary school teachers of the students. The results showed that students started learning English at the average age 7.9-years-old and about 80% of the students were receiving a variety of private English instruction. In line with expectations, tutored students outperformed non-tutored students on the English achievement test. In addition most of the teachers, as well as students, thought it helpful to learn English through private English instruction. One implication from the results suggests that to ensure quality English language teaching at public schools, the government should put forth efforts to nurture qualified English teachers through intensive teacher training.