Answer: Random assignment
Step-by-step explanation:
Random sampling and random assignment both implies that selection process is randomized such that each observation has equal chances of being selected.
However, in the case of random sampling, observations to be used in the experiment or research are being randomized. WHILE in random assignment, the observations or participants to be used are already selected, however, the placement of observations into different experimental groups are assigned randomly.
Therefore, in a research to determine whether students tend to receive higher scores on essays if they are encouraged to submit a draft than if they are not so encouraged, a random assignment is required because all participants or observations in the study needs to be adequately selected because it is important that all participants are used to writing essays and not those who detest essays no matter the condition.