jmc

There are $3$ ways to pick the first student, $2$ ways to pick the second student, and $1$ way to pick the last student, for a total of $3!=3\times 2\times 1=6$ ways to line the students up. Only $1$ of those ways is alphabetical. Thus, the probability is $\frac{1}{6}$ or $\boxed{\frac{1}{6}}$