To find the total number of students in the seventh grade, we can use the information that 9 students represent 25% of the total seventh-grade students.
Let \( x \) be the total number of seventh-grade students. According to the problem, 25% of \( x \) is equal to 9 students. We can express this mathematically as:
\[ 0.25x = 9 \]
To solve for \( x \), divide both sides by 0.25:
\[ x = \frac{9}{0.25} \]
Calculating the right side:
\[ x = 9 \div 0.25 = 9 \times 4 = 36 \]
Therefore, the total number of students in the seventh grade is \( \boxed{36} \).