We are looking for a standardized test to measure students' vocabulary size to guide designing speaking tasks. The speaking tasks will be designed in line with CEFR and Pearson GSE topics. The target group is young adults and adults. Thank you.
Pearson's Teacher Toolkit might be useful to sort the vocabulary and determine the level / difficulty of the vocabulary items you will use in designing the tasks.
In our institution, we use it to determine the vocabulary items for the placement and proficiency tests.