2,000). Ini berarti hipotesis nol ditolak dan hipotesis penelitian diterima. Dengan demikian dapat disimpulkan "Pengaruh penguasaan derivasi bahasa Inggris memberikan pengaruh yang positif terhadap prestasi belajar Vocabulary siswa di SLTP Maarif NU Tegal kelas VIII Tahun Pelajaran 2009/2010." Inggris : KUSNANI. "The Effect of Derivation Comprehension toward Vocabulary Achievement in SLTP Maarif NU Tegal for VIII Grade Students in the Academic Year 2009/2010". Thesis. 2010. Strata 1 Program. Program of English Department, Faculty of Teacher Training and Educational, Pancasakti University Tegal. Key word : Derivation comprehension, vocabulary achievement. The objective of this thesis is to find out clearly describing whether there is positive effect of Derivational English Mastery of achievement vocabulary learning for VIII grade student at SLTP Maarif NU Tegal in the academic year 2009/2010. Based on the background, identification and limitation of the research, so can be formulation of the research is "Is there positive effect of derivation mastery toward vocabulary achievement learning for VIII grade students of SLTP Maarif NU Tegal in the academic year 2009/2010?" The population of this research is the VIII grade students, the total number 361 student and consists of 195 boys and 166 girls. The writer uses stratified random sampling technique. The sample of research is 60 students and consists of two groups 30 students and the second group 30 students. The data analysis of this research is rasted by using t-test, to test different in the level of significant of 5% gained information that there is different vocabulary achievement learning between derivational mastery students of tall with derivation mastery student of low. Based on the result of data analysis t-ratio is 2,717 and t-table with the degree of freedom is 58, and in level of significant of 5% t-table is 2,000 that t-ratio is higher than t-table (2,717 > 2,000) this is the alternative hypothesis refused and the noll hypothesis is accepted. By such can be find out that students who have derivation mastery tall has vocabulary achievement learning better than students who has derivational mastery low so that conclusion that derivational mastery gives positif effect toward vocabulary achievement for VIII grade students of SLTP Maarif NU Tegal in academic year 2009/2010." />