To convert the percentage of sixth-graders who play sports (35%) into a fraction, we can start by expressing 35% as a fraction over 100:
\[ 35% = \frac{35}{100} \]
Next, we need to simplify this fraction. The greatest common divisor (GCD) of 35 and 100 is 5. So we can divide both the numerator and the denominator by 5:
\[ \frac{35 \div 5}{100 \div 5} = \frac{7}{20} \]
So, the fraction of sixth-graders who play sports is \(\frac{7}{20}\).
Thus, the correct answer is:
A) \( \frac{7}{20} \)