In a school reading program, a certain number of the fifth-grade students are assigned a twelfth-grade reading partner. No twelfth grader is assigned more than one fifth-grade partner. If $\frac{3}{4}$ of all the fifth graders are paired with $\frac{2}{3}$ of all the twelfth graders, what fraction of the total number of fifth and twelfth graders are involved in the reading program?