Answer
The student is wrong. The answer is the opposite sign: $-\dfrac{3}{2}$
Work Step by Step
The formula to find the slope is $\dfrac{y_2-y_1}{x_2-x_1}$
Plugging in the values, we'll get:
$\dfrac{-4-2}{1-(-3)}\rightarrow \dfrac{-6}{4}\rightarrow -\dfrac{3}{2}$
The student didn't get it right. It is possible they mixed up the order in the numerator or the denominator:
$\dfrac{y_1-y_2}{x_2-x_1} \space\text{or}\space \dfrac{y_2-y_1}{x_1-x_2}$
Doing that will result in the wrong sign. It is important to note, however, that mixing up the order in both the numerator and denominator won't change the value and is still valid:
$\dfrac{y_2-y_1}{x_2-x_1}=\dfrac{y_1-y_2}{x_1-x_2}\checkmark$
