The study skills and learning motivation were assumed to be the significant factors that positively influence the learning process of school learners. In this study, the study skills were measured by 7 sub-skills of self-managements(15 items), listening and participating in class(15 items), task-solving(13 items), effectively reading(15 items), report writing(15 items), information processing(15 items), and test-taking(14 items). Learning motivation were composed of academic self-efficacy(26 items) and academic failure tolerance(17 items). The purpose of this study were to examine the grade level differences of following relationships between these process variables and learning outcomes for middle school, high school, and college students: 1)The inter-correlations among the use of study skills, learning motivation level, and academic achievements, 2)the relative importance and combined effects of these process variables(9 factors) on academic achievements, and 3)the academic achievements level differences in the use of study skills and the level of learning motivation. For this study, two questionnaires of study skills and learning motivation were administered to 265 middle school students, 285 high school students, and 329 college students that were purposively sampled in Cheongju and other area. Their GPA were also obtained from their instructors. The major findings in this study were as followings. First, lower the grade level was, higher the correlations between learning process variables(study skills and learning motivation) and academic achievements were. Second, the differences between higher achiever and lower achiever in both the use of study skills and the level of learning motivation were showed relatively widest in middle school students, and relatively narrowest in college students. Third. the level that higher achievers in all grade levels utilized study skills in their school learning was less than 2.9, and the levels of learning motivation was less than 2.7 on 4-point scale. College students showed more positive behavior than secondary school students in the use of study skills. Fourth, the combined effects of study skills and learning motivation on academic achieve- ments were 34 percent in middle school students, 23 percent in high school students, and 10 percent in college students. Relatively important factors that explained the academic achieve- ments were found to be the test-taking skill, self-efficacy, and task-solving in middle and high school students, and task-solving in college students.