4. Allocate eight model student quotas to four classes, Jia, Yi, Bing, and Ding, with each class getting at least one quota. Then the probability that Class Jia gets exactly two quotas is $\qquad$
4. $\frac{2}{7}$.

Distribute eight outstanding student quotas to four classes, Jia, Yi, Bing, and Ding, with each class getting at least one quota. The number of different distribution schemes is $\mathrm{C}_{7}^{3}=35$ (using the partition method: arrange the eight quotas in a row, and insert three partition boards in the seven gaps formed by them. Each way of inserting the partition boards corresponds to a distribution scheme, and vice versa).

Among these, the number of distribution schemes where Class Jia gets exactly two quotas is $\mathrm{C}_{5}^{2}=10$ (equivalent to distributing six quotas to three classes, with each class getting at least one quota).
Therefore, the required probability is $\frac{10}{35}=\frac{2}{7}$.