According to the data of Baidu Library, the formula for calculating the average grade of grade four is as follows: average grade = (sum of grades in all subjects)/(number of subjects). Suppose there are three subjects: mathematics, Chinese and English. The scores are 80, 90 and 85 respectively. Then the average score is calculated as follows: average score =(80+90+85)/3=255/3=85. Therefore, the average score of grade four students is 85. Please note that this is a simplified example, and the actual situation may involve the weighted calculation of more subjects and more grades.