In this section, I describe wage dynamics and labor market experience from the tracking data. As mentioned, the survey collected information on employment for each job in which our students have ever engaged. Table 5 summarizes some key variables. On average, our sample individuals began work slightly before age 17. Their average educational attainment is a little below high school completion. These observations imply that students are likely to have had some work experience (though they are short term) before completing their schooling. In some cases, therefore, both general and specific human capital seems to accumulate at the same time.

Figure 2 shows years of tenure of the first work in the sample. The distribution is highly skewed with the mean of 1.52 years. The median is close to zero. Figure 3 shows years of experience (defined as the period from the first time they worked to now). Though the distribution is similarly skewed, the mean is 3.86 years. Given the fact that our sample consists of the youth whose average age is about 20, both years of tenure and experience are small.

Table 6 Panel A shows summary statistics of log monthly earnings of each work, the first to tenth. The last row shows statistics for the most recent job (including the current one). If a former student worked as a family member and did not receive any salary, it will not show up in the table. The number of observations differs between the first job and the latest job because some of them did not receive a salary at the first job but were paid thereafter.

The table shows a clear picture of wage dynamics in our sample. On average, wage increases monotonically if students change jobs but the variation of wages decreases monotonically. This is probably because only those who have better opportunities can switch to the next job, and this process is selective. Interestingly, the minimum level of wage increases while the maximum decreases simultaneously. The variability of wages tends to become smaller along with occupational changes.

Panel B of the table shows similar statistics of the SY 1999/00 Gr-6 sample. In Panel A, it is possible that a mixture of two cohorts (SY 1999/00 and SY 2004/05 & 20005/06) created such artifacts. A more homogeneous group from the grade 6 cohort of SY 1999/00 also shows the same characteristics, which supports the robustness of the above findings. That is, the average wage tends to increase and the variance tends to decrease monotonically as they change jobs.<sup>14</sup> Next, I describe the effect of labor market experience on wage growth. The vertical axis in Figure 4 shows difference in log earnings between the latest and first jobs. Experience, measured in years by the time between the start of the first work and the beginning of 2011, is on the horizontal axis. Figure 4a shows experience effects for relatively educated and less educated workers. I use high school completion as the threshold. Figure 4b differentiates the sample by mathematics test scores. Interestingly, the relatively more schooled group reaches 40% growth at the 7-th year, while the relatively less schooled group only reaches 20% growth in the same span of time. In the latter, concavity sets in after 5 years. Mathematics test score also predicts the slope of wage growth. Those who scored higher than 75 percent in grade 6 show a higher wage growth starting from the very beginning of work experience than those who scored less than 50 percent.

> 14 At this stage, it is not clear whether only good performers can upgrade their occupations or work experience generally raises wages.

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