Let the total number of students at McCord Middle School be \( x \).
Since 300 students represent 60% of the total student body, we can set up the equation:
\[ 0.6x = 300 \]
To find \( x \), divide both sides by 0.6:
\[ x = \frac{300}{0.6} \]
Calculating that gives:
\[ x = 500 \]
Therefore, the total number of students attending McCord Middle School is 500 students.