Why a paired-sample t-test is more appropriate in testing pretest and posttest scores than an interdependent t-test?

Welcome =D

Thank you for your explanation.

Paired-sample t-tests compare scores on two different variables
but for the same group of cases; independent-sample t-tests compare scores on the same variable
but for two different groups of cases. The links between a subject's pretest and posttest are why the procedure's name refers to paired samples.