This isn't an assignment but I would like to interpret the graph in a proper way. For example, I try to calculate the percent difference between the two medians of the left-preferent ones (see Table 1): 11.35kg and 10.40kg. But the result (11.35kg - 10.40kg/ 10.40kg x 100% = + 9.1%) does not correspond to the Q2 median of the corresponding boxplot of the left-handed children of the 1st grade. The y axis represents the performances of the children using their dominant hand for each grade of primary school.